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

#define PI 3.14159265358979323846264338327950L

int main(void)
{
    int a, b, h, m;
    scanf("%d%d%d%d", &a, &b, &h, &m);

    long double rad = PI * 2 * ((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));

    return 0;
}