#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define ott(i,l,r) for (register int i = l; i <= r; i ++)
#define tto(i,l,r) for (register int i = r; i >= l; i --)
using namespace std;
int read () {
	int x = 0; bool f = false; char c = getchar ();
	while (!isdigit (c)) f |= (c == '-'), c = getchar ();
	while (isdigit (c)) x = (x << 3) + (x << 1) + (c ^ 48), c = getchar ();
	return f ? -x : x;
}
typedef long long ll;
typedef long double ld;
const int N = 2e5 + 110, M = 1 << 17;
int n, m, siz;
vector <pair <int, int> > g[M];
ld f[N]; char ch[17];
int cnt[N];
int main () {
	n = read (), m = read (), siz = 1 << m;
	ott (s, 0, siz - 1) {
		int len = 1 << __builtin_popcount (s);
		g[s].resize (len);
		for (int t = s; t; t = (t - 1) & s) g[s][-- len].fi = t;
		g[s][-- len].fi = 0; assert (!len);
	}
	ott (i, 1, n) {
		int s = 0; scanf ("%s", ch);
		ott (j, 0, m - 1) if (ch[j] ^ '0') s |= 1 << j;
		++ g[siz - 1][s].se;
	}
	
	tto (s, 0, siz - 2) {
		int k; ott (j, 0, m - 1) if (!(s >> j & 1)) {
			k = j; break;
		}
		int t = s | (1 << k);
		for (auto x : g[s]) cnt[x.fi] = 0;
        for (auto x : g[t]) cnt[s & x.fi] += x.se;
        for (auto &x : g[s]) x.se = cnt[x.fi];
	}
	ott (s, 0, siz - 1) {
        if ((s + 1) & 1) continue;
        int c = n - g[s][0].se - g[s][(int)g[s].size () - 1].se;
        if (!c) f[s] = 1.0;
        else {	
            for (auto x : g[s]) {
				int t = x.fi;
                if (t && t ^ s)
                	f[s] += f[t] * x.se;
            }
            f[s] /= c;
        }
    }
    printf ("%.12Lf\n", f[siz - 1]);
	return 0;
}