/*ex4_2
series2*/

# include <stdio.h>
# include <math.h>
int main(void){
    //各文字の箱を作って読み取り
    int l_hand,s_hand,hour,minute;
    scanf("%d %d %d %d",&l_hand,&s_hand,&hour,&minute);
    //二本の針の差を0以上pi以下で計算
    //2*M_PI*(60*hour+minute)/(12*60)は時針の進んだ角度
    //2*M_PI*minute/60は分針の進んだ角度
    long double diff=2*M_PI*(60*hour+minute)/(12*60)-2*M_PI*minute/60;
    //余弦定理を用いて端点の差を計算
    printf("%.20f\n",sqrt((l_hand*l_hand+s_hand*s_hand-2*l_hand*s_hand*cos(diff))));
    return 0;
}