#include<bits/stdc++.h>
#define INF 1000000000
using namespace std;

#define MAXN 805
#define MAXM 80500
#define fix 700

const int S=800,T=801;
int n,m,c[15][65],mk[15][65],tot;

int head[MAXN],cnt=1;
struct Edge{
    int to,flow,cap,next,cost,from;
}e[MAXM];
inline void insert(int a,int b,int f,int c) {
    e[++cnt].next=head[a];head[a]=cnt;e[cnt].to=b;e[cnt].flow=f;e[cnt].cap=0;e[cnt].cost=c;e[cnt].from=a;
    e[++cnt].next=head[b];head[b]=cnt;e[cnt].to=a;e[cnt].flow=0;e[cnt].cap=0;e[cnt].cost=-c;e[cnt].from=b;
}

queue<int> q;int z[MAXN],bk[MAXN];bool f[MAXN];
int updata(){
    int a=INF;
    for(int i=bk[T];i;i=bk[e[i].from]) {
        a=min(a,e[i].flow-e[i].cap);
    }
    for(int i=bk[T];i;i=bk[e[i].from]) {
        e[i].cap+=a;e[i^1].cap-=a;
    }
    return a;
}
int spfa() {
    int k;memset(z,0x3f3f,sizeof(z));
    q.push(S);z[S]=0;f[S]=1;
    while(!q.empty()) {
        k=q.front();q.pop();
        for(int i=head[k];i;i=e[i].next) {
            if(z[e[i].to]>z[k]+e[i].cost&&e[i].flow>e[i].cap) {
                bk[e[i].to]=i;z[e[i].to]=e[i].cost+z[k];
                if(!f[e[i].to]){q.push(e[i].to);f[e[i].to]=1;}
            }
        }
        f[k]=0;
    }
    if(z[T]<0x3f3f3f3f) k=updata();
    else return INF;
    return z[T]*k;
}
int MSMF() {
    int f,ret=0;
    while((f=spfa())!=INF) ret+=f;
    return ret;
}

int main() {
    scanf("%d%d",&m,&n);
    for(int j=1;j<=n;j++) for(int i=1;i<=m;i++) {
        scanf("%d",&c[i][j]);mk[i][j]=++tot;
    }
    for(int i=1;i<=m;i++) for(int j=1;j<=n;j++) {
        for(int k=1;k<=n;k++) insert(k+fix,mk[i][j],1,j*c[i][k]);
        insert(mk[i][j],T,1,0);
    }
    for(int i=1;i<=n;i++) insert(S,i+fix,1,0);
    printf("%.2lf\n",(double)MSMF()/n);
    return 0;
}