学步园

#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#define inf 0x7fffffff
using namespace std;
inline int read(){
    int x=0,f=1;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}
struct edge{int from,to,next,v,c;}e[200001];
int t[61][10];
int n,m,cnt=1,ans,T=2001,head[2005],from[2005],dis[2005];
inline void ins(int u,int v,int w,int c){
	e[++cnt]=(edge){u,v,head[u],w,c};head[u]=cnt;
	e[++cnt]=(edge){v,u,head[v],0,-c};head[v]=cnt;
}
inline bool spfa(){
	int t=0,w=1,q[10001];
	bool inq[10001];
	memset(inq,0,sizeof(inq));
	for(int i=0;i<=T;i++)dis[i]=inf;
	dis[0]=0;q[0]=0;inq[0]=1;
	while(t!=w){
		int now=q[t++];if(t==T)t=0;
		for(int i=head[now];i;i=e[i].next)
			if(e[i].v&&dis[e[i].to]>dis[now]+e[i].c){
				dis[e[i].to]=dis[now]+e[i].c;
				from[e[i].to]=i;
				if(!inq[e[i].to]){
					inq[e[i].to]=1;
					q[w++]=e[i].to;
					if(w==T)w=0;
				}
			}
		inq[now]=0;
	}
	if(dis[T]==inf)return 0;
	return 1;
}
inline 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^1].v+=x;ans+=e[i].c*x;
	}
}
int main(){
	n=read();m=read();
    for(int i=1;i<=m;i++)
    	for(int j=1;j<=n;j++)
        	scanf("%d",&t[i][j]);
    for(int i=1;i<=n*m;i++)
    	ins(0,i,1,0);
    for(int i=n*m+1;i<=n*m+m;i++)
        ins(i,T,1,0);
    for(int i=1;i<=n;i++)
    	for(int j=1;j<=m;j++)
        	for(int k=1;k<=m;k++)
            	ins((i-1)*m+j,n*m+k,1,t[k][i]*j);
    while(spfa())mcf();
	printf("%.2lf",(double)ans/m);
    return 0;
}