N=int(input())
A=list(map( int,input().split()))
dp=[0]*(N+1)
for i in range(1,N+1):
    try:
        dp[i]=max(dp[i-1],dp[i-2]+A[i])
    except IndexError:
        dp[i]=max(dp[i-1],A[i-1])
print(dp[-1])