#include "bits/stdc++.h"
#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef complex<ld> cd;
 
typedef pair<int, int> pi;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;
 
typedef vector<int> vi;
typedef vector<ld> vd;
typedef vector<ll> vl;
typedef vector<pi> vpi;
typedef vector<pl> vpl;
typedef vector<cd> vcd;

template<class T> using pq = priority_queue<T>;
template<class T> using pqg = priority_queue<T, vector<T>, greater<T>>;
 
#define FOR(i, a, b) for (int i=a; i<(b); i++)
#define F0R(i, a) for (int i=0; i<(a); i++)
#define FORd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define F0Rd(i,a) for (int i = (a)-1; i >= 0; i--)
#define trav(a,x) for (auto& a : x)
#define uid(a, b) uniform_int_distribution<int>(a, b)(rng)
 
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
#define ins insert

template<class T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }
 
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifdef DEBUG
#define dbg(x...) cerr << "\e[91m"<<__func__<<":"<<__LINE__<<" [" << #x << "] = ["; _print(x); cerr << "\e[39m" << endl;
#else
#define dbg(x...)
#endif


const int MOD = 1000000007;
const char nl = '\n';
const int MX = 17; 

int N;
int cnt[1<<MX];
double dp[1<<MX];
int cm = 0;
double ans = 0;

void rem(int b) {
    cm ^= 1<<b;
    for (int s = cm; ; s = (s-1)&cm) {
        cnt[s] += cnt[s|(1<<b)];
        if (s == 0) break;
    }
}

void add(int b) {
    for (int s = cm; ; s = (s-1)&cm) {
        cnt[s] -= cnt[s|(1<<b)];
        if (s == 0) break;
    }
    cm ^= 1<<b;
}

void go(int b) {
    if (b == -1) {
        int cur = 0;
        for (int s = (cm-1)&cm; s; s = (s-1)&cm) {
            cur += cnt[s];
        }
        if (cur == 0) {
            if (cm & (1<<(N-1))) ans += dp[cm];
            return;
        }
        for (int s = (cm-1)&cm; s; s = (s-1)&cm) {
            dp[s] += dp[cm] * cnt[s] / cur;
        }
        return;
    }
    go(b-1);
    rem(b);
    go(b-1);
    add(b);
}


void solve() {
    int M; cin >> M >> N;
    string S[M]; F0R(i, M) cin >> S[i];
    F0R(i, M) {
        int cur = 0;
        F0R(j, N) {
            cur *= 2; cur += S[i][j] - '0';
        }
        cnt[cur]++;
    }
    dp[(1<<N)-1] = 1; 
    cm = (1<<N)-1;
    go(N-2);
    cout << setprecision(30) << ans << nl;
}
 
int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);

    int T = 1;
//    cin >> T;
    while(T--) {
        solve();
    }

	return 0;
}