#include<stdio.h>
#include<string.h>
#include<math.h>
int main(){
  
 long double a,b,h,m;
 long double d1,d2,xs,ys,xl,yl;
 long double PI,dis;
  PI=3.14159265358979L;
 
  scanf("%Lf %Lf %Lf %Lf",&a,&b,&h,&m);
 
  
  xs=a*(double)sin((PI)*(30*h+m/2)/180);
  ys=a*cos((PI)*(30*h+m/2)/180);
  
  xl=b*sin((PI)*(6*m)/180);
  yl=b*cos((PI)*(6*m)/180);
  
  dis=hypot((xs-xl),(ys-yl));
  
  printf("%.10Lf",dis);
  
  return 0;
}