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

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