N = int(input())
V = list(map(int,input().split()))

dp = [[-1] * 2 for i in range(N + 1)]
dp[0][0] = 0
for i in range(N):
    dp[i + 1][0] = max(dp[i])
    dp[i + 1][1] = dp[i][0] + V[i]
    
print(max(dp[-1]))