func_code_string: #include <bits/stdc++.h>   using namespace std;   const double pi = 3.1415926536;   const long long INF = 1e18;   const int32_t M = 1e6 + 7;   const int32_t MM = 998244353;   long long a, b, c, d;   void solve() {     cin >> a >> b >> c >> d;     double p, q, x;     p = (double)a / b;     q = (double)c / d;     x = (1 - p) * (1 - q);     x = 1 - x;     cout << fixed << setprecision(12);     cout << p / x;   }   signed main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     long long t = 1;     while (t--) solve();     return 0;   }   