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

else:
    print(v[0])