#coding: utf-8
##yuki_45

n=int(raw_input())
s=map(int,raw_input().split())

dp=[0 for i in xrange(1008)]
res=0
for i  in xrange(n):
 temp=max(dp[i+2]+s[i],dp[i+1]+s[i])
 dp[i+4]=temp
 res=max(res,temp)
 
print res