func_code_string: #include <bits/stdc++.h>   double a, b, c, d, x, y;   int main() {     scanf( %lf%lf%lf%lf , &a, &b, &c, &d);     x = a / b;     y = c / d;     printf( %lf , x / (1.0 - (1.0 - x) * (1.0 - y)));   }   