#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", sqrt(rsq));
	
	return 0;
}