line = input().split()
pos = 0
def readInt():
    global pos, line
    if pos >= len(line):
        line = input().split()
        pos = 0
    pos += 1
    return int(line[pos - 1])
a = readInt()
b = readInt()
x = readInt()
y = readInt()
print(min(abs(b-a),abs(abs(b-a)-abs(x-y)),abs(a-x)+abs(b-y)))