#include <bits/stdc++.h>
#include <bits/extc++.h>

typedef long long int ll;
typedef unsigned long long int ull;
typedef std::pair<int,int> pii;
typedef std::vector<int> vec;

using namespace std;

#define __rep(i,a,b,c) for(int i=(a);i!=(b);i+=(c))
#define _rep(i,a,b) for(int i=(a);i>=(b);i--)
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define Yes cout << "Yes" << endl
#define No cout << "No" << endl
#define End return 0
#define blockId(x) ((x)/BLOCK_SIZE)

namespace Anschluss_zeit {
	const int MAXN = 500000;
	namespace IO {
		void read(){}
		template<typename T,typename... Types>
		void read(T& first, Types&... args){
			T x = 0, f = 1;char c = getchar();
			while (!isdigit(c)) {if (c == '-') f = -1;c = getchar();}
			while (isdigit(c))x = (x << 3) + (x << 1) + (c^'0'), c = getchar();
			first = x * f;
			read(args...);
		}
		template<typename T>
		void _print(T x) {if (x < 0) x = (~x + 1), putchar('-');if (x > 9) _print(x / 10);putchar(x % 10 + '0');}
		void _print(string s) {int l = s.length();for (int i = 0; i < l; i++)putchar(s[i]);}
		void print(){}
		void eoln(){putchar('\n');}
		template<typename T,typename... Types>
		void print(T first, Types... args){_print(first);putchar(' ');print(args...);}
		template<typename T,typename... Types>
		void println(T first, Types... args){print(first,args...);eoln();}
	};
};
using namespace Anschluss_zeit;
using namespace IO;

#define INF 1e16

struct edge{
	int nxt, to;
	ll c, w;
	//表示 一条连往v的边的容量为c，代价w
} e[10 * MAXN];

int cnt = 1, then[MAXN];
ll dis[MAXN];
bitset<MAXN> vis, inq;

queue<int> q;

void _add(int u, int v, ll c, ll w){e[++cnt]=(edge){then[u], v, c, w}; then[u]=cnt;}
void add(int u, int v, ll c, ll w){_add(u, v, c, w); _add(v, u, 0, -w);}

int S, T, cur[MAXN];

bool dinic_bfs(){//SPFA
	while(!q.empty()) q.pop();
	copy(then, then + MAXN, cur);
	fill(dis, dis + MAXN, INF);
	dis[S] = 0; q.push(S); inq[S] = 1;
	inq.reset();
	while(!q.empty()){
		int t = q.front(); q.pop();
		inq[S] = 0;
		for(int i = cur[t]; i; i = e[i].nxt){
			int c = e[i].c, v = e[i].to;
			if(c > 0 && dis[v] > dis[t] + e[i].w){
				dis[v] = dis[t] + e[i].w;
				if(!inq[v]) q.push(v), inq[v] = 1;
			}
		}
	}
	return dis[T] < INF;
}

ll dinic_dfs(int x, ll flow){
	if(x == T) return flow;
	ll rf = flow; vis[x] = 1;
	for(int i = cur[x]; i; i = e[i].nxt){
		if(rf <= 0) break;
		cur[x] = i;
		ll rf_x = e[i].c; int v = e[i].to;
		if(rf_x > 0 && dis[v] == dis[x] + e[i].w && !vis[v]){
			ll transfer = dinic_dfs(v, min(rf_x, rf));
			rf -= transfer;
			e[i].c -= transfer;
			e[i ^ 1].c += transfer;
		}
	}
	vis[x] = 0;
	return flow - rf;
}

pii dinic(){
	int mx, mn;
	while(dinic_bfs()){
		int flow = dinic_dfs(S, INF);
		mx += flow;
		mn += dis[T] * flow;
	}
	return make_pair(mx, mn);
}

int n, m, c[100][100], id;

signed main() {
	read(m, n);
	S = 0; T = n * m + n + 1;
	rep(i, 1, n){
		rep(j, 1, m){
			read(c[i][j]);
		}
	}
	rep(i, 1, n * m) add(S, i, 1, 0);
	rep(i, 1, m){
		rep(j, 1, n){
			rep(k, 1, n){
				add((i - 1) * n + k, i * n + j + n * m, 1, c[j][i] * k);
			}
		}
	}
	rep(i, 1, n) add(n * m + i, T, 1, 0);
	printf("%.2lf",(double) dinic().second / (double) n);
	return 0;
}

Dinic算法。