#include <bits/stdc++.h>

using namespace std;

const int MAX_N = 500000 + 5;

int N;
long double p[MAX_N], f[MAX_N];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    
    cin >> N;
    for (int i = 1; i <= N; i ++) {
        cin >> p[i];
    }
    static int q[MAX_N];
    int hd = 0, tl = -1;
    q[++ tl] = N + 1;
    auto w = [&](int i, int j) -> long double {
        return (1.0 - p[j]) * i + f[j];
    };
    long double ans = 0;
    for (int i = N; i > 0; i --) {
        while (hd < tl && w(i, q[hd + 1]) > w(i, q[hd])) hd ++;
        f[i] = w(i, q[hd]) * p[i]; ans = max(ans, f[i]);
        while (tl > hd && (f[i] - f[q[tl - 1]]) / (p[i] - p[q[tl - 1]]) < (f[i] - f[q[tl]]) / (p[i] - p[q[tl]])) tl --;
        q[++ tl] = i;
    }
    cout << fixed << setprecision(20) << ans << '\n';
    
    return 0;
}