#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")

#include <bits/stdc++.h>

#define ll long long
#define ld double
using namespace std;

const int N = 5e3 + 5, lg = 19, mod = 998244353;

int n, k;
bool vis[N][2 * N + 10];
ld p[N], dp[N][2 * N + 10];
/*
ld solve(int idx, int cnt) {
    if(idx == n) {
        return cnt >= N + k;
    }

    if(vis[idx][cnt]) return dp[idx][cnt];
    vis[idx][cnt] = 1;
    // ld op1 = solve(idx + 1, cnt);
    ld op1 = 0;
    ld op2 = p[idx] * solve(idx + 1, cnt + 1) + (1.0 - p[idx]) * solve(idx + 1, cnt - 1);
    return dp[idx][cnt] = max(op1, op2);
}

*/

void solve() {
    for(int i = N + k; i < N + N; i++) {
        dp[n][i] = 1;
    }
    for(int i = 0; i < N + k; i++) dp[n][i] = 0;

    for(int i = n - 1; i >= 0; i--) {
        // cout << "i " << i << endl;
        for(int j = 1; j + 1 < N + N; j++) {
            dp[i][j] = p[i] * dp[i + 1][j + 1] + (1.0 - p[i]) * dp[i + 1][j - 1];
        }
    }
}


int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    cin >> n >> k;
    for (int i = 0; i < n; ++i) {
        cin >> p[i];
    }
    sort(p, p + n);
    ld ans = 0;
    solve();
    for(int i = 0; i < n; i++) {
        ans = max(ans, dp[i][N]);
    }
    cout << fixed << setprecision(10) << ans << '\n';
    return 0;
}