#include <bits/stdc++.h>
using namespace std;

#ifdef _RUTHEN
#include "debug.hpp"
#else
#define show(...) true
#endif

using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
template <class T> using V = vector<T>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N;
    cin >> N;
    V<double> A(N - 1);
    rep(i, N - 1) cin >> A[i];
    double ans = 1000;
    rep(i, N - 1) ans *= (1000 - A[i]) / 1000;
    ans = 1000 - ans;
    cout << fixed << setprecision(15) << ans << '\n';
    return 0;
}