/*
  kadai4_2 colon
  unomi
*/
#include <stdio.h>
#include <math.h>

#define PI 3.1415926535

int main(void){
    long double h_length=0, m_length=0, hour=0, minute=0, h_rad=0, m_rad=0, diff_rad=0, ans_dist=0;
    // h_length(A),m_length(B),hour(H),minute(M) の入力を取得
    scanf("%Lf %Lf %Lf %Lf",&h_length, &m_length, &hour, &minute);

    // 時針が動いた角度(ラジアン)
    h_rad = (360 * (hour/12.0 + minute/60.0)) * PI / 180.0;
    // 分針が動いた角度(ラジアン)
    m_rad = (360 * (minute/60.0)) * PI /180.0;
    // 時針と分針が成す角の角度(ラジアン)
    diff_rad = h_rad - m_rad;

    // 余弦定理を用いて、端点の距離を計算
    ans_dist = sqrt(h_length*h_length + m_length*m_length - 2*h_length*m_length*cos(diff_rad));

    printf("%10.10Lf\n",ans_dist);
    return 0;
}