N = int(input())
M = int(input())
x = int(input())
y = int(input())
if M > N:
    a = (N - x)
    b = (M - y)
    if a < y < x < b:
        print (a)
    elif y < a < b < x:
        print (y)
    elif b < y < a < x:
        print (b)
    else:
        print (x)
else:
    a = (M - x)
    b = (N - y)
    if a < y < x < b:
        print (a)
    elif y < a < b < x:
        print (y)
    elif b < y < a < x:
        print (b)
    else:
        print (x)