import sys
input = sys.stdin.readline

N = int(input())
A = list(map(int, input().split()))
B = []

for i in range(0, 2*N, 2):
    B.append(A[i]-A[i+1])

B_acc = [0]

for Bi in B:
    B_acc.append(B_acc[-1]+Bi)

ans = -float('inf')

for i in range(N+1):
    ans = max(ans, 2*B_acc[i]-B_acc[N])

print(ans)