#include <bits/stdc++.h>
int main(void) {
  int a, b, h, m;
  scanf("%d%d%d%d", &a, &b, &h, &m);
  long double rad = 3.14159265358979323846264338327950L * 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;
}
