#include <bits/stdc++.h>   using namespace std;   int main() {     int a, b;     cin >> a >> b;     if ((a >= 0 && b < 0) || (a < 0 && b >= 0)) {       cout <<  -1 ;       return 0;     }     if (a == 0 && b == 0) {       cout <<  -1 ;       return 0;     }     if (a < 0 && b < 0) {       cout <<  -1 ;       return 0;     }     if (b == 0 && a > 0) {       cout <<  -1 ;       return 0;     }     if (a == b) {       cout << a;       return 0;     }     if (a > 0 && b > 0) {       if (b > a) {         cout <<  -1 ;         return 0;       } else {         int k1 = (a - b) / (2 * b);         double x1 = (double)(a - b) / (2 * k1);         int k2 = (a + b) / (2 * b);         double x2 = (double)(a + b) / (2 * k2);         cout << setprecision(10) << min(x1, x2);       }     }     return 0;   }   