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