#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;
}