#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>

int max(int a,int b){
  if(a > b) return a;
  else return b;
}
int min(int a, int b){
  if(a < b) return a;
  else return b;
}

#define PI 3.14159265358979323846264338327950

int main(){

  int a,b,h,m;
  scanf("%d%d%d%d",&a, &b, &h, &m);

  double angle = abs( ((double)h + (double)m/60) * 30 - (double)m * 6 );
  double rad = (angle /180)* PI;

  //printf("%.10f ",h);
  double ans = sqrt((double)a*a + (double)b*b -(double)2*a*b*cos(rad));
  printf("%.11f",ans);

  return 0;
}
