from math import cos, sqrt, radians
A, B, H, M = map(int, input().split())
Md = M * 6
Hd = (H * 30) + ((M/60) * 30)
Cd = (Hd - Md)
As = A ** 2
Bs = B ** 2
D = 2 * A * B
X = sqrt(As + Bs - (D * cos(radians(Cd))))
print(X)