#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

int main(){

    int N;
    cin >> N;
    vector<long double> A(N-1);
    for (int i=0; i<N-1; i++) cin >> A[i];
    long double ans=1000;
    for (int i=0; i<N-1; i++){
        ans *= (1000.l - A[i]) / 1000.l;
    }

    cout << setprecision(18) << 1000.l - ans << endl;

    return 0;
}