/* ex4_2
   tamayama  */

#include<stdio.h>
#include<math.h>
#define PI 3.1415926535

double dist(int length_A,int length_B,int hour,int minute);
int main(void){
    int A,B,H,M;
    double distance;
    scanf("%d %d %d %d",&A,&B,&H,&M);
    distance = dist(A,B,H,M);
    printf("%.10f\n",distance);
    return 0;
}

double dist(int length_A,int length_B,int hour,int minute){
    double rad_A,rad_B;
    double rad;
    double rad_diff;
    double length;

    rad_A = (double)((hour * 30 + minute * 0.5) * PI / 180.0);    /*12時の位置から時針の角度*/
    rad_B = (double)(6 * minute * PI / 180.0);    /*12時の位置から分針の角度*/
    rad_diff = rad_A - rad_B;
    rad = fabs(rad_diff);    /*時針と分針の角度を求める*/
    length = sqrt(length_A * length_A + length_B * length_B - 2 * length_A * length_B * cos(rad));    /*余弦定理*/
    return(length);
}