#include <bits/stdc++.h>
int main(void) {
  double a, b, n, m;
  scanf("%lf%lf%lf%lf", &a, &b, &n, &m);
  n = 30.0 * (n + m / 60.0);
  m = m * 6.0;
  printf("%.10f",
         sqrt(a * a + b * b - 2 * a * b * cos((n - m) / 360.0 * 2.0 * M_PI)));
  return 0;
}
