#include <bits/stdc++.h>
#define inf (0x7f7f7f7f)
#define Max(a, b) ((a) > (b) ? (a) : (b))
#define Min(a, b) ((a) < (b) ? (a) : (b))
#define pi pair<double, double>
typedef long long ll;
using namespace std;
template <class T>
inline void read(T &x){
    int ch = 0, f = 0; x = 0;
    for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = 1;
    for(; isdigit(ch); ch = getchar()) x = x * 10 + ch - 48;
    if(f) x = -x;
}

double p[501000];

deque <pi> q;

double f(int i, pi it) {
    return it.first * i + it.second;
}

double g(pi q1, pi q2) {
    return (q2.second - q1.second) / (q1.first - q2.first);
}

int main(){
    int n;
    read(n);
    for (int i = 1; i <= n; i ++) 
        scanf("%lf", p + i);
    double cur = p[n] * n;
    q.push_back(make_pair(1 - p[n], cur));
    for (int i = n - 1; i >= 1; i --) {
        while (q.size() > 1) {
            pi q1 = q.front(); q.pop_front();
            pi q2 = q.front();
            if (f(i, q1) < f(i, q2))
                continue;
            else {
                q.push_front(q1);
                break;
            }
        }
        cur = max(cur, p[i] * f(i, q.front()));
        pi qnow = make_pair(1 - p[i], cur);
        while (q.size() > 1) {
            pi q2 = q.back(); q.pop_back();
            pi q1 = q.back();
            if (g(q1, q2) < g(q2, qnow))
                continue;
            else {
                q.push_back(q2);
                break;
            }
        }
        q.push_back(qnow);
    }
    cout << fixed << setprecision(20) << cur << '\n';
    return 0;
}