#include <bits/stdc++.h>
using namespace std;
int main() {
  const double PI = 3.14159265358979323846;
  double A, B, H, M;
  double x1, x2, y1, y2, angleH, angleM, ans;
  cin >> A >> B >> H >> M;
  angleH = -2 * PI * H / 12 + PI / 2 - M * PI / 6 / 60;
  angleM = -2 * PI * M / 60 + PI / 2;
  x1 = A * cos(angleH);
  y1 = A * sin(angleH);
  x2 = B * cos(angleM);
  y2 = B * sin(angleM);
  ans = pow(pow(abs(x2 - x1), 2) + pow(abs(y2 - y1), 2), 0.5);
  cout << ans;
  return 0;
}
