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#include<bits/stdc++.h>

#define db double

using namespace std;

const int N = 25003;

db T[2][N], V[N];

inline db mx ( db d1, db d2) {
    if (d1 < d2) return d2;
    return d1;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n , t;
    cin>>n>>t;
    string s;
    for (int i = 0; i < n; ++i) {
        cin>>s;
        db a = 0, d = 0.1;
        a += (db) (s[0] - '0');
        for (int j = 2; j < s.length(); ++j) {
            a += (db) (s[j] - '0') * d;
            d *= 0.1;
        }
        V[i] = a;
    }

    sort(V, V + n, greater<db>());
    int  m = 1, k = 1, l, il = 0, ir = 0;
    int borderLeft = (n-t) / 2, borderRight = t + ((n-t+1) / 2);
    T[k][0] = 1.;

    db pmax = 0., pRight = 0.;

    for (int i = 1; i <= n; ++i) {
        l = k ^ 1;

        db p = 0.;

        T[l][il] = 0.;
        // cout<<"##### "<<i<<' '<<V[i-1]<<'\n';
        for (int j = il; j <= ir; ++j) {
            T[l][j] += (1. - V[i-1]) * T[k][j];
            T[l][j+1] = V[i-1] * T[k][j];

            // cout<<j<<' '<<T[l][j]<<'\n';

            if (2 * j >= t + i) {
                p += T[l][j];
            }
        }

        // cout<<ir+1<<' '<<T[l][ir+1]<<'\n';

        if (n - 2 * i < t) {
            ++il;
        }
        if (2 * i - n <  t) {
            ++ir;
            if (2 * ir >= t + i) p += T[l][ir];
        } else {
            pRight += T[l][ir+1];
        }

        // cout<<"p: "<< p << " pright: "<<pRight<<'\n';
        pmax = mx(pmax, p + pRight);
        k ^= 1;
    }

    cout << fixed << setprecision(9) << pmax << '\n';
}