A, B, H, M = map(float, input().split())

import math
PI = math.pi
radA = (2.0 * PI * (H + M / 60.0)) / 12.0
radB = (2.0 * PI * M) / 60.0
print(math.hypot(A * math.cos(radA) - B * math.cos(radB),
                 A * math.sin(radA) - B * math.sin(radB)))