#include <iostream>
#define rep(i, l, n) for (int i = (l); i < (n); i++)
using namespace std;

int main(void) {
	int n;	cin >> n;

	double m = 1000.0, d = 1000.0;
	double ans = 0;
	rep(i, 0, n - 1) {
		int a;	cin >> a;
		ans += a * (d / m);
		d = 1000.0 - ans;
	}
	printf("%.9f\n", ans);

	return 0;
}