def solve(X,Y):
    if X==Y==0:
        return 0
    elif X==0 or Y==0:
        return 1
    elif abs(X)+abs(Y)<=3:
        return 1
    else:
        return 2
A,B,C,D=map(int,input().split())
X=A-C
Y=B-D
print(solve(X,Y))