https://www.acmicpc.net/problem/2156
n=int(input())
mlist=[int(input()) for _ in range(n)]
dp=[0]*n
dp[0]=mlist[0]
if n>1:
dp[1]=mlist[0]+mlist[1]
if n>2:
dp[2]=max(dp[1], mlist[0]+mlist[2], mlist[1]+mlist[2])
if n>3:
for i in range(3,n):
dp[i]=max(mlist[i]+mlist[i-1]+dp[i-3], mlist[i]+dp[i-2],dp[i-1])
print(max(dp))