#!/usr/bin/env python3
import math
def f(a):
    dp = [None] * (len(a) // 2 + 1)
    dp[0] = 0
    for i in range(len(a) // 2):
        dp[i + 1] = dp[i] + a[2 * i] - a[2 * i + 1]
    return dp
def main():
    n = int(input())
    a = list(map(int, input().split()))
    l = f(a)
    r = list(reversed(f(list(reversed(a)))))
    print(max([l[i] + r[i] for i in range(n + 1)]))
if __name__ == "__main__":
    main()