#include <bits/stdc++.h>

#define i64 long long

using namespace std;

const int N = 5e5 + 10;

int n, hh, tt = -1;
pair<double, double> q[N];
double p[N], f[N];

double solve(pair<double, double> a, int i) {
	return a.second + a.first * i;
}

int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n; i ++) scanf("%lf", &p[i]);
	
	for (int i = 1; i <= n + 1; i ++) p[i] = 1 - p[i];
	
	f[n + 1] = 0;
	q[++ tt] = make_pair(p[n + 1], f[n + 1]);
	for (int i = n; i >= 1; i --) {
		while (hh + 1 <= tt && solve(q[tt - 1], i) > solve(q[tt], i)) tt --;
		f[i] = solve(q[tt], i) * (1 - p[i]);
		pair<double, double> Nw = make_pair(p[i], f[i]);
		while (hh + 1 <= tt && 
		(Nw.second - q[tt].second) * (q[tt].first - q[tt - 1].first) <
		(q[tt].second - q[tt - 1].second) * (Nw.first - q[tt].first)
		) tt --;
		q[++ tt] = Nw;
	}
	
	double ans = 0;
	for (int i = 1; i <= n; i ++) ans = max(ans, f[i]);
	
	printf("%.9lf", ans);
	
	return 0;
}