#include <cstdio>
#include <cstring>
#include <algorithm>

const int maxnd = 10100, maxe = 100005;

int m, n, time[65][15], S, T;
int head[maxnd], next[maxe], from[maxe], to[maxe], w[maxe], cap[maxe], flow[maxe], lb;
int d[maxnd], p[maxnd], c[maxnd], que[maxnd], head_, tail, h;
char inq[maxnd];

inline void ist(int aa, int ss, int ww, int ca) {
	to[lb] = ss;
	from[lb] = aa;
	next[lb] = head[aa];
	head[aa] = lb;
	w[lb] = ww;
	cap[lb] = ca;
	++lb;
	
	to[lb] = aa;
	from[lb] = ss;
	next[lb] = head[ss];
	head[ss] = lb;
	w[lb] = -ww;
	cap[lb] = 0;
	++lb;
}
inline bool spfa(int & co) {
	memset(d, 0x3c, sizeof d);
	memset(inq, 0, sizeof inq);
	head_ = tail = 0;
	que[tail++] = S;
	inq[S] = 1;
	d[S] = 0;
	c[S] = 2147483647;
	while (head_ != tail) {
		h = que[head_++];
		inq[h] = 0;
		if (head_ == T + 3) {
			head_ = 0;
		}
		for (int j = head[h]; j != -1; j = next[j]) {
			if (flow[j] < cap[j] && d[to[j]] > d[h] + w[j]) {
				d[to[j]] = d[h] + w[j];
				p[to[j]] = j;
				c[to[j]] = std::min(c[h], cap[j] - flow[j]);
				if (!inq[to[j]]) {
					inq[to[j]] = 1;
					que[tail++] = to[j];
					if (tail == T + 3) {
						tail = 0;
					}
				}
			}
		}
	}
	if (d[T] == 0x3c3c3c3c) {
		return false;
	}
	co += d[T] * c[T];
	for (int i = T; i != S; i = from[p[i]]) {
		flow[p[i]] += c[T];
		flow[p[i] ^ 1] -= c[T];
	}
	return true;
}
inline int mcmf(void) {
	int co = 0;
	while (spfa(co));
	return co;
}

int main(void) {
	//freopen("in.txt", "r", stdin);
	memset(head, -1, sizeof head);
	memset(next, -1, sizeof next);
	scanf("%d%d", &m, &n);
	T = n * (m + 1) + 1;
	for (int i = 1; i <= n; ++i) {
		ist(S, i, 0, 1);
		for (int j = 1; j <= m; ++j) {
			scanf("%d", time[i] + j);
		}
	}
	for (int j = 1; j <= m; ++j) {
		for (int k = 1; k <= n; ++k) {
			for (int i = 1; i <= n; ++i) {
				ist(i, j * n + k, time[i][j] * k, 1);
			}
			ist(j * n + k, T, 0, 1);
		}
	}
	printf("%.2f\n", (double)mcmf() / (double)n);
	return 0;
}