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

ans = max(abs(x), abs(y))
if x*x2 + y*y2 == 0 and dist(0,0,x2,y2) < dist(0,0,x,y) and dist(x,y,x2,y2)  < dist(0,0,x,y):
    ans += 1
print ans