func_code_string: #include <bits/stdc++.h>   using namespace std;   int N;   double A[100001];   double dp[100001];   int main() {     scanf( %d , &N);     for (int i = 1; i <= N; i++) scanf( %lf , A + i);     double ans = 0.0;     for (int i = 1; i <= N; i++)       ans += A[i] + 2 * (dp[i] = (dp[i - 1] + A[i - 1]) * A[i]);     printf( %.9f n , ans);     return 0;   }   