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