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

#define PI 3.14159265358979323846264338327950L

int main(void){
  int a,b,h,m;
  scanf("%d%d%d%d",&a,&b,&h,&m);
  
  long double rad = PI * 2 * ((long double) h / 12.0 + ((long double)m /60.0) / 12.0 - (long double)m/60.0);
  long double rsq = (long double)(a*a+b*b) -(long double)(2*a*b)*cosl(rad);
  printf("%20.20Lf\n",sqrtl(rsq));
  return 0;
}