import math
 
PI = math.pi
A, B, H, M = map(int, input().split())
 
arg_a = (float(H) + float(M)/60) / 12.0 * 360
arg_b = float(M) / 60.0 * 360
 
 
C = math.sqrt(A*A + B*B - 2*A*B* math.cos((arg_a-arg_b)/360*2*PI))
print(C)