#include<stdio.h>
#include<math.h>
#define PI 3.14159265358979323846264338327950L
int main()
{
    int a,b,h,m;
   scanf("%d %d %d %d",&a,&b,&h,&m);
   long double rad=2*PI*((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));
}