func_code_string: #include <bits/stdc++.h>   using namespace std;   double p[100005], e1[100005], e2[100005];   int main() {     int n;     scanf( %d , &n);     for (register int i = 1; i <= n; ++i) scanf( %lf , p + i);     for (register int i = 1; i <= n; ++i) {       e1[i] = (e1[i - 1] + 1) * p[i];       e2[i] = e2[i - 1] + (e1[i - 1] + e1[i - 1] + 1) * p[i];     }     printf( %.15lf , e2[n]);     return 0;   }   