#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <atcoder/modint>

using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(int)(n); i++)


const i64 INF = 1001001001001001001;
using modint = atcoder::static_modint<1000000007>;


int main(){
	int N; cin >> N;
	vector<i64> A(N-1);
	rep(i,N-1) cin >> A[i];
	vector<double> dp(N);
	dp[0] = 1000.0;
	rep(i,N-1) dp[i+1] = dp[i] * (1000.0 - A[i]) / (1000.0);
	cout.precision(10);
	cout << fixed;
	cout << (1000.0 - dp[N-1]) << '\n';
    return 0;
}


struct ios_do_not_sync{
    ios_do_not_sync(){
        std::ios::sync_with_stdio(false);
        std::cin.tie(nullptr);
    }
} ios_do_not_sync_instance;