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

int main(){
  double A,B,H,M;
  scanf("%lf %lf %lf %lf",&A,&B,&H,&M);
  double thetaH,thetaM,ans2;
  thetaH = 2*M_PI/12*(H + M/60);
  thetaM = 2*M_PI/60*M;
  
  ans2 = A*A + B*B - 2*A*B*cos(fabs(thetaH - thetaM));
  printf("%.20lf\n",sqrt(ans2));
}