import sequtils,strutils

var
  n = parseInt readLine stdin
  vs = stdin.readLine.split.map parseInt
  dp = 0.repeat n
  
dp[0] = vs[0]
if n > 1: dp[1] = vs[1]
if n > 2: dp[2] = vs[2] + vs[0]
if n > 3:
  for i in 3..n-1:
    dp[i] = vs[i] + dp[i-2].max dp[i-3]
echo max dp