from collections import *

N = int(input())
A = list(map(int, input().split()))
B = [0] * N
for i in range(N):
    B[i] = - A[2 * i] + A[2 * i + 1]

ans = sum(B)
val = ans
for i in range(N):
    val -= B[i] * 2
    ans = max(ans, val)
print(ans)