#include <bits/stdc++.h>

using namespace std;

#define iter(v) v.begin(), v.end()
#define SZ(v) int(v.size())
#define pb emplace_back
#define ff first
#define ss second

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#ifdef zisk
void debug() { cerr << "\n"; }
template<class T, class ... U>
void debug(T a, U ... b){ cerr << a << " ", debug(b...); }
template<class T>
void pary(T l, T r) {
	while (l != r) cerr << *l << " ", l++;
	cerr << "\n";
}
#else
#define debug(...) void()
#define pary(...) void()
#endif

template<class A, class B>
ostream &operator<<(ostream &o, pair<A, B> p) {
	return o << '(' << p.ff << ',' << p.ss << ')';
}

using ld = double;
struct Line {
	ld a = 0, b = 0;
	ld operator()(int x) {
		return a * x + b;
	}
};
int n;
#define lc 2 * id
#define rc 2 * id + 1
struct SegTree {
	vector<Line> seg;
	SegTree(): seg(4 * (n + 1)) {}
	void modify(Line ln, int L = 0, int R = n, int id = 1) {
		int M = (L + R) / 2;
		if (seg[id](M) < ln(M))
			swap(seg[id], ln);
		//debug("modify", L, R, M, seg[id].a, seg[id].b, seg[id](M), "|", ln.a, ln.b, ln(M));
		if (L == R) return;
		if (seg[id].a > ln.a) modify(ln, L, M, lc);
		else modify(ln, M + 1, R, rc);
	}
	ld query(int x, int L = 0, int R = n, int id = 1) {
		if (L == R) return seg[id](x);
		int M = (L + R) / 2;
		if (x <= M) return max(seg[id](x), query(x, L, M, lc));
		else return max(seg[id](x), query(x, M + 1, R, rc));
	}
};

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

	cin >> n;
	vector<ld> p(n + 1);
	for (int i = 1; i <= n; i++)
		cin >> p[i];
	
	SegTree seg;
	seg.modify(Line({1 - p[n], p[n] * n}));
	for (int i = n - 1; i >= 1; i--) {
		ld dp = seg.query(i);
		seg.modify(Line({1 - p[i], p[i] * dp}));
		//debug("test", i, 1 - p[i], p[i] * dp, dp);
	}
	ld ans = seg.query(0);
	cout << fixed << setprecision(15) << ans << "\n";

}