/**************************************************************

     Problem: 1070

     User: Tunix

     Language: C++

     Result: Accepted

     Time:464 ms

     Memory:6012 kb

 ****************************************************************/

 //BZOJ 1070

 #include<cmath>

 #include<vector>

 #include<cstdio>

 #include<cstring>

 #include<cstdlib>

 #include<iostream>

 #include<algorithm>

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

 #define F(i,j,n) for(int i=j;i<=n;++i)

 #define D(i,j,n) for(int i=j;i>=n;--i)

 #define pb push_back

 #define CC(a,b) memset(a,b,sizeof(a))

 using namespace std;

 int getint(){

     int v=,sign=; char ch=getchar();

     while(!isdigit(ch)) {if(ch=='-') sign=-; ch=getchar();}

     while(isdigit(ch))  {v=v*+ch-''; ch=getchar();}

     return v*sign;

 }

 const int N=,M=,INF=~0u>>;

 const double eps=1e-;

 /*******************template********************/

 int n,m,ans,tim[][];

 struct edge{int from,to,v,c;};

 struct Net{

     edge E[M];

     int head[N],next[M],cnt;

     void ins(int x,int y,int z,int c){

         E[++cnt]=(edge){x,y,z,c};

         next[cnt]=head[x]; head[x]=cnt;

     }

     void add(int x,int y,int z,int c){

         ins(x,y,z,c); ins(y,x,,-c);

     }

     int from[N],Q[M],S,T,d[N];

     bool inq[N];

     bool spfa(){

         int l=,r=-;

         F(i,S,T) d[i]=INF;

         d[S]=; Q[++r]=S; inq[S]=;

         while(l<=r){

             int x=Q[l++];

             inq[x]=;

             for(int i=head[x];i;i=next[i])

                 if (E[i].v && d[x]+E[i].c<d[E[i].to]){

                     d[E[i].to]=d[x]+E[i].c;

                     from[E[i].to]=i;

                     if(!inq[E[i].to]){

                         Q[++r]=E[i].to;

                         inq[E[i].to]=;

                     }

                 }

         }

         return d[T]!=INF;

     }

     void mcf(){

         int x=INF;

         for(int i=from[T];i;i=from[E[i].from])

             x=min(x,E[i].v);

         for(int i=from[T];i;i=from[E[i].from]){

             E[i].v-=x;

             E[i^].v+=x;

             ans+=x*E[i].c;

         }

 //      ans+=x*d[t];

     }

     void init(){

         m=getint(); n=getint(); cnt=;

         F(i,,n)

             F(j,,m) tim[i][j]=getint();

         S=; T=n+n*m+;

         F(i,,n) add(S,i,,);

         F(i,n+,n+n*m) add(i,T,,);

         F(i,,n)

             F(j,,m)

                 F(k,,n)//枚举这 第i辆车是第j个人修的第k辆

                     add(i,j*n+k,,(n-k+)*tim[i][j]);

         ans=;

         while(spfa()) mcf();

         printf("%.2lf\n",double(ans)/n);

     }

 }G1;

 int main(){

 #ifndef ONLINE_JUDGE

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

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

 #endif

     G1.init();

     return ;

 }