N = int(input())
V = list(map(int,input().split()))
dp = [[0]*2 for _ in range(N+1)]
dp[0][1] = -10**18
for i in range(N):
    dp[i+1][0] = max(dp[i])
    dp[i+1][1] = dp[i][0] + V[i]

print(max(dp[N]))