N = int(input())
A = list(map(int,input().split()))
from itertools import accumulate
L = list(accumulate([A[i] - A[i+1] for i in range(0,2*N,2) ], initial = 0))
R = list(accumulate([A[-1-i] - A[-2-i] for i in range(0,2*N,2)], initial = 0))
ans = max(L[i]+R[-1-i] for i in range(N))
print(ans)