 #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;
}
