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