#include <bits/stdc++.h>

 using namespace std;

 #define INIT() ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

 #define Rep(i,n) for (int i = 0; i < (n); ++i)

 #define For(i,s,t) for (int i = (s); i <= (t); ++i)

 #define rFor(i,t,s) for (int i = (t); i >= (s); --i)

 #define ForLL(i, s, t) for (LL i = LL(s); i <= LL(t); ++i)

 #define rForLL(i, t, s) for (LL i = LL(t); i >= LL(s); --i)

 #define foreach(i,c) for (__typeof(c.begin()) i = c.begin(); i != c.end(); ++i)

 #define rforeach(i,c) for (__typeof(c.rbegin()) i = c.rbegin(); i != c.rend(); ++i)

 #define pr(x) cout << #x << " = " << x << "  "

 #define prln(x) cout << #x << " = " << x << endl

 #define LOWBIT(x) ((x)&(-x))

 #define ALL(x) x.begin(),x.end()

 #define INS(x) inserter(x,x.begin())

 #define UNIQUE(x) x.erase(unique(x.begin(), x.end()), x.end())

 #define REMOVE(x, c) x.erase(remove(x.begin(), x.end(), c), x.end()); // ?? x ?????? c

 #define TOLOWER(x) transform(x.begin(), x.end(), x.begin(),::tolower);

 #define TOUPPER(x) transform(x.begin(), x.end(), x.begin(),::toupper);

 #define ms0(a) memset(a,0,sizeof(a))

 #define msI(a) memset(a,inf,sizeof(a))

 #define msM(a) memset(a,-1,sizeof(a))

 #define MP make_pair

 #define PB push_back

 #define ft first

 #define sd second

 template<typename T1, typename T2>

 istream &operator>>(istream &in, pair<T1, T2> &p) {

     in >> p.first >> p.second;

     return in;

 }

 template<typename T>

 istream &operator>>(istream &in, vector<T> &v) {

     for (auto &x: v)

         in >> x;

     return in;

 }

 template<typename T>

 ostream &operator<<(ostream &out, vector<T> &v) {

     Rep(i, v.size()) out << v[i] << " \n"[i == v.size()];

     return out;

 }

 template<typename T1, typename T2>

 ostream &operator<<(ostream &out, const std::pair<T1, T2> &p) {

     out << "[" << p.first << ", " << p.second << "]" << "\n";

     return out;

 }

 inline int gc(){

     static const int BUF = 1e7;

     static char buf[BUF], *bg = buf + BUF, *ed = bg;

     if(bg == ed) fread(bg = buf, , BUF, stdin);

     return *bg++;

 } 

 inline int ri(){

     int x = , f = , c = gc();

     for(; c<||c>; f = c=='-'?-:f, c=gc());

     for(; c>&&c<; x = x* + c - , c=gc());

     return x*f;

 }

 template<class T>

 inline string toString(T x) {

     ostringstream sout;

     sout << x;

     return sout.str();

 }

 inline int toInt(string s) {

     int v;

     istringstream sin(s);

     sin >> v;

     return v;

 }

 //min <= aim <= max

 template<typename T>

 inline bool BETWEEN(const T aim, const T min, const T max) {

     return min <= aim && aim <= max;

 }

 typedef long long LL;

 typedef unsigned long long uLL;

 typedef pair< double, double > PDD;

 typedef pair< int, int > PII;

 typedef pair< int, PII > PIPII;

 typedef pair< string, int > PSI;

 typedef pair< int, PSI > PIPSI;

 typedef set< int > SI;

 typedef set< PII > SPII;

 typedef vector< int > VI;

 typedef vector< double > VD;

 typedef vector< VI > VVI;

 typedef vector< SI > VSI;

 typedef vector< PII > VPII;

 typedef map< int, int > MII;

 typedef map< int, string > MIS;

 typedef map< int, PII > MIPII;

 typedef map< PII, int > MPIII;

 typedef map< string, int > MSI;

 typedef map< string, string > MSS;

 typedef map< PII, string > MPIIS;

 typedef map< PII, PII > MPIIPII;

 typedef multimap< int, int > MMII;

 typedef multimap< string, int > MMSI;

 //typedef unordered_map< int, int > uMII;

 typedef pair< LL, LL > PLL;

 typedef vector< LL > VL;

 typedef vector< VL > VVL;

 typedef priority_queue< int > PQIMax;

 typedef priority_queue< int, VI, greater< int > > PQIMin;

 const double EPS = 1e-;

 const LL inf = 0x7fffffff;

 const LL infLL = 0x7fffffffffffffffLL;

 const LL mod = 1e9 + ;

 const int maxN = 1e3 + ;

 const LL ONE = ;

 const LL evenBits = 0xaaaaaaaaaaaaaaaa;

 const LL oddBits = 0x5555555555555555;

 int N, M, board[maxN][maxN];

 int Fmax, Smax;

 stack< PII > st;

 void update(int area) {

     if(area < ) return;

     if(area > Fmax) {

         Smax = Fmax;

         Fmax = area;

     }

     else if(area > Smax) Smax = area;

 }

 int main(){

     //freopen("MyOutput.txt","w",stdout);

     //freopen("input.txt","r",stdin);

     //INIT();

     scanf("%d%d", &N, &M);

     For(i, , N) {

         while(!st.empty()) st.pop();

         board[i][] = -; // 哨兵

         For(j, , M) {

             scanf("%1d", &board[i][j]);

             if(board[i][j]) board[i][j] += board[i - ][j];

         }

         board[i][M + ] = -; // 哨兵 

         For(j, , M + ) {

             while(!st.empty() && st.top().ft > board[i][j]) {

                 PII tmp = st.top(); st.pop();

                 int w = j - tmp.sd + tmp.sd - st.top().sd - ;

                 update(tmp.ft * w);

                 update(tmp.ft * (w - ));

                 update((tmp.ft - ) * w);

             }

             st.push(PII(board[i][j], j));

         }

     }

     printf("%d\n", Smax);

     return ;

 }