#include <bits/stdc++.h>
int main() {
  double A, B, H, M;
  scanf("%lf %lf %lf %lf", &A, &B, &H, &M);
  double ax, ay, bx, by, pi, dis;
  pi = atan(1.0) * 4.0;
  ax = A * sin((H / 6 + M / 360) * pi);
  ay = sqrt(A * A - ax * ax);
  if (H >= 3 && H < 9) ay = -ay;
  bx = B * sin((M / 30) * pi);
  by = sqrt(B * B - bx * bx);
  if (M >= 15 && M < 45) by = -by;
  dis = sqrt((ax - bx) * (ax - bx) + (ay - by) * (ay - by));
  printf("%.16f\n", dis);
  return 0;
}
