#include<cstdio>

 #include<cstring>

 #include<cstdlib>

 #include<cmath>

 #include<algorithm>

 using namespace std;

 int n,m,st,ed,ans;

 struct node

 {

     int x,y,c,d,next,other;

 }a[];int len,last[];

 void ins(int x,int y,int c,int d)

 {

     int k1,k2;

     k1=++len;

     a[len].x=x;a[len].y=y;a[len].c=c;a[len].d=d;

     a[len].next=last[x];last[x]=len;

     k2=++len;

     a[len].x=y;a[len].y=x;a[len].c=;a[len].d=-d;

     a[len].next=last[y];last[y]=len;

     a[k1].other=k2;

     a[k2].other=k1;

 }

 int head,tail,list[],dis[],pre[],cc[];

 bool v[];

 bool spfa()

 {

     memset(cc,,sizeof(cc));cc[st]=;

     memset(v,false,sizeof(v));v[st]=true;

     memset(dis,0x3F,sizeof(dis));dis[st]=;

     head=;tail=;list[]=st;pre[st]=;

     while(head!=tail)

     {

         int x=list[head];

         for(int k=last[x];k;k=a[k].next)

         {

             int y=a[k].y;

             if( (a[k].c>) && (dis[y]>dis[x]+a[k].d) )

             {

                 cc[y]= min(cc[x],a[k].c);

                 dis[y]=dis[x]+a[k].d;

                 pre[y]=k;

                 if(!v[y])

                 {

                     v[y]=true;

                     list[tail++]=y;

                     if(tail==ed+) tail=;

                 }

             }

         }

         v[x]=false;

         head++; if(head==ed+)head=;

     }

     if(dis[ed]>)return false;

     ans+=dis[ed]*cc[ed];

     int x=ed;

     while(x!=st)

     {

         int k=pre[x];

         a[k].c-=cc[ed];a[a[k].other].c+=cc[ed];

         x=a[k].x;

     }

     return true;

 }

 int map[][];

 int main()

 {

     scanf("%d%d",&m,&n);

     len=;memset(last,,sizeof(last));

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

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

         {

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

         }

     st=n+m*n+;ed=st+;

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

     {

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

         {

             for(int k=;k<=n;k++)

             {

                 ins(i,j*n+k,,map[i][j]*(n-k+));

             }

         }

     }

     for(int i=;i<=n;i++)ins(st,i,,);

     for(int i=n+;i<=n+n*m;i++)ins(i,ed,,);

     ans=;

     while(spfa());

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

     return ;

 }