def dist(a,b,c,d):
    return ((a - c) ** 2 + (b - d) ** 2) ** 0.5
    
x, y = map(int, raw_input().split())
x2, y2 = map(int, raw_input().split())

ans = max(abs(x), abs(y))
if abs(dist(0, 0, x2, y2) + dist(x2, y2, x, y) - dist(0, 0, x, y)) < 1e-7:
    ans += 1
print ans