#include <bits/stdc++.h>   using namespace std;   int i;   double a, b, c, d, base, top, mid, x11, x22, y11, y22, minim1, minim2, maxim1,       maxim2;   int main() {     scanf( %lf%lf%lf%lf , &a, &b, &c, &d);     base = 0.0;     top = 1000000000.0;     for (i = 1; i <= 100; i++) {       mid = (base + top) / 2.0;       x11 = a - mid;       x22 = a + mid;       y11 = d - mid;       y22 = d + mid;       minim1 = min(min(x11 * y11, x11 * y22), min(x22 * y11, x22 * y22));       maxim1 = max(max(x11 * y11, x11 * y22), max(x22 * y11, x22 * y22));       x11 = b - mid;       x22 = b + mid;       y11 = c - mid;       y22 = c + mid;       minim2 = min(min(x11 * y11, x11 * y22), min(x22 * y11, x22 * y22));       maxim2 = max(max(x11 * y11, x11 * y22), max(x22 * y11, x22 * y22));       if (maxim1 < minim2 || maxim2 < minim1)         base = mid;       else         top = mid;     }     printf( %.9lf n , top);   }   