import bisect,collections,itertools,math,functools,heapq
import sys
#sys.setrecursionlimit(10**6)
def I(): return int(sys.stdin.readline().rstrip())
def IN(): return int(input())
def LIN(): return list(map(int, input().split()))
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LF(): return list(map(float,sys.stdin.readline().rstrip().split()))
def SI(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())

"""
方針
dp
"""

N=I()
V=LI()

dp = [[0,0] for _ in range(N+1)]

for i in range(N):
    v = V[i]
    dp[i+1][0] = max(dp[i][1] + v, dp[i][0])
    dp[i+1][1] = max(dp[i][0], dp[i][1])
print(max(dp[N]))