#include 
     
      #include 
      
       #include 
       
        #include 
        
         #include 
         
          #include 
          
           using namespace std;bool fun(double l1,double r1,double l2,double r2){ return (l1 <= r2 && l1 >= l2) || (l2 >= l1 && l2 <= r1);}int main() { double a,b,c,d; cin >> a >> b >> c >> d; double r = 1000000000.0; double l = 0; for(int i = 0;i < 1000;i++){ double m = l + (r - l) /2.0; double a1 = (a-m)*(d-m); double a2 = (a-m)*(d+m); double a3 = (a+m)*(d-m); double a4 = (a+m)*(d+m); double l1 = min(min(a1,a2),min(a3,a4)); double r1 = max(max(a1,a2),max(a3,a4)); a1 = (c-m)*(b-m); a2 = (c-m)*(b+m); a3 = (c+m)*(b-m); a4 = (c+m)*(b+m); double l2 = min(min(a1,a2),min(a3,a4)); double r2 = max(max(a1,a2),max(a3,a4)); if(fun(l1,r1,l2,r2)){ r = m; } else{ l = m; } } printf("%.10f\n",l); return 0; }