N = int(input())
V = list(map(int,input().split()))
dp = [[0] * 2 for _ in range(N)]
dp[0][0] = 0
dp[0][1] = V[0]

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