/* 3295 */

 #include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <cstdlib>

 #include <queue>

 using namespace std;

 typedef struct {

     char m[][];

     char x, y;

     char s, c;

 } node_t;

 typedef struct subNode_t {

     char x, y;

     subNode_t() {}

     subNode_t(char xx, char yy) {

         x = xx; y = yy;

     }

 } subNode_t;

 bool visit[][];

 node_t beg, cur;

 int n, m, cnt;

 char dir[][] = {

     -,,,-,,,,

 };

 queue<node_t> Q;

 queue<subNode_t> q;

 inline bool check(char x, char y) {

     return x< || x>=n || y< || y>=m;

 }

 void remove(char x, char y, char cl) {

     char i, j, k;

     subNode_t nd;

     ++cur.s;

     cur.m[x][y] = ;

     visit[x][y] = true;

     --cur.c;

     q.push(subNode_t(x, y));

     while (!q.empty()) {

         nd = q.front();

         q.pop();

         for (i=; i<; ++i) {

             x = nd.x + dir[i][];

             y = nd.y + dir[i][];

             if (check(x, y) || visit[x][y])

                 continue;

             if (cur.m[x][y] == cl) {

                 cur.m[x][y] = ;

                 visit[x][y] = true;

                 --cur.c;

                 q.push(subNode_t(x, y));

             }

         }

     }

 }

 node_t shift() {

     char i, j, k, r;

     bool flag;

     node_t nd;

     // copy from cur

     nd.s = cur.s;

     nd.c = cur.c;

     nd.x = cur.x;

     nd.y = cur.y;

     memset(nd.m, , sizeof(nd.m));

     // fall down

     r = ;

     for (j=; j<m; ++j) {

         k = n-;

         for (i=n-; i>=; --i)

             if (cur.m[i][j])

                 nd.m[k--][r] = cur.m[i][j];

         if (k < n-)

             ++r;

     }

     return nd;

 }

 char bfs() {

     char i, j, k;

     node_t nd;

     while (!Q.empty())

         Q.pop();

     memset(visit, false, sizeof(visit));

     for (i=; i<n; ++i) {

         for (j=; j<n; ++j) {

             if (beg.m[i][j] && !visit[i][j]) {

                 cur = beg;

                 remove(i, j, beg.m[i][j]);

                 nd = shift();

                 Q.push(nd);

             }

         }

     }

     while (!Q.empty()) {

         beg = Q.front();

         Q.pop();

         if (beg.c == )

             return beg.s;

         memset(visit, false, sizeof(visit));

         for (i=; i<n; ++i) {

             for (j=; j<m; ++j) {

                 if (beg.m[i][j] && !visit[i][j]) {

                     cur = beg;

                     remove(i, j, beg.m[i][j]);

                     nd = shift();

                     Q.push(nd);

                 }

             }

         }

     }

     return ;

 }

 int main() {

     int i, j, k;

     #ifndef ONLINE_JUDGE

         freopen("data.in", "r", stdin);

     #endif

     while (scanf("%d%d",&n,&m) != EOF) {

         cnt = ;

         beg.s = ;

         for (i=; i<n; ++i) {

             for (j=; j<m; ++j) {

                 scanf("%d", &k);

                 beg.m[i][j] = k;

                 if (k)

                     ++cnt;

             }

         }

         beg.c = cnt;

         k = bfs();

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

     }

     return ;

 }