MOD = 10 ** 9 + 7
INF = 10 ** 10
import sys
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)

def main():
    n = int(input())
    a = list(map(int,input().split()))
    tot = sum(a)

    cuml = [0] * (n + 1)
    cumr = [0] * (n + 1)

    for i in range(n):
        cuml[i + 1] = cuml[i] + a[2 * i]
    
    for i in range(n - 1,-1,-1):
        cumr[i] = cumr[i + 1] + a[2 * i + 1]
    
    ans = 0
    for i in range(n + 1):
        ans = max(ans,2 * cuml[i] + 2 * cumr[i] - tot)
    
    print(ans)

if __name__ =='__main__':
    main()