백준 2455 파이썬

a_1, b_1 = map(int, input().split())

a_2, b_2 =map(int, input().split())

a_3,b_3 = map(int, input().split())

a_4,b_4 =map(int, input().split())

num = []

num.append(b_1)

num.append(num[0]- a_2 + b_2)

num.append(num[1] - a_3 + b_3)

num.append(num[2] - a_4 + b_4)

print(max(num))