#include<bits/stdc++.h>
#define FILE "read"
#define MAXN 100010
#define INF (int)1e9
using namespace std;
struct node{int y,next,v,w;}e[MAXN<<1];
int n,m,S,T,cnt,ans,len(1),a[110][110],Link[MAXN],vis[MAXN],dis[MAXN],id[110][110],LN[MAXN],LE[MAXN],flow[MAXN];
queue<int>q;
inline int read(){
	int x=0,f=1;  char ch=getchar();
	while(ch>'9'||ch<'0')  {if(ch=='-')  f=-1;  ch=getchar();}
	while(ch>='0'&&ch<='9')  {x=x*10+ch-'0';  ch=getchar();}
	return x*f;
}
void insert(int x,int y,int v,int w){
	e[++len].next=Link[x];Link[x]=len;e[len].y=y;e[len].v=v;e[len].w=w;
	e[++len].next=Link[y];Link[y]=len;e[len].y=x;e[len].v=0;e[len].w=-w;
}
bool spfa(){
	memset(vis,0,sizeof(vis));
	memset(dis,10,sizeof(dis)); 
	int oo=dis[0];q.push(S);dis[S]=0;vis[S]=1;flow[S]=INF;  
	while(!q.empty()){
		int x=q.front();  q.pop();  vis[x]=0;
		for(int i=Link[x];i;i=e[i].next)if(dis[x]+e[i].w<dis[e[i].y]&&e[i].v){
			dis[e[i].y]=dis[x]+e[i].w; flow[e[i].y]=min(flow[x],e[i].v);
			LN[e[i].y]=x; LE[e[i].y]=i;
			if(!vis[e[i].y])  q.push(e[i].y),vis[e[i].y]=1;
		}
	}
	if(dis[T]==oo)  return 0;
	ans+=flow[T]*dis[T];
	for(int i=T;i!=S;i=LN[i]) e[LE[i]].v-=flow[T],e[LE[i]^1].v+=flow[T];
	return 1;
}
int main(){
	freopen(FILE".in","r",stdin);
	freopen(FILE".out","w",stdout);
	m=read();  n=read();  S=++cnt;  T=++cnt;
	for(int i=1;i<=n;++i)for(int j=1;j<=m;++j)a[i][j]=read();
	for(int i=1;i<=m;++i)for(int j=1;j<=n;++j)
		id[i][j]=++cnt,insert(S,id[i][j],1,0);
	for(int i=1;i<=n;++i){
		int x=++cnt; insert(x,T,1,0);
		for(int j=1;j<=m;++j)for(int k=1;k<=n;++k)insert(id[j][k],x,1,k*a[i][j]);
	}
	while(spfa());
	printf("%.2lf\n",(double)ans/n);
	return 0;
}