N = int(input())
value = list(map(int,input().split()))
if N == 1:
    print(value[0])
    
if N >=2:   
    dp=[-1]*N
    dp[0] = value[0]
    dp[1] = max(value[0],value[1])
    for i in range(2,N):
        dp[i] = max(dp[i-1],dp[i-2]+value[i])
    print(dp[N-1])