import strutils, sequtils, algorithm, math

var
  n = readLine(stdin).parseInt()
  vSeq = readLine(stdin).split(' ').map(parseInt)
  dp = newSeq[int](1002)

dp[0] = vSeq[0]
if n > 1:
  dp[1] = vSeq[1]
if n > 2:
  dp[2] = dp[0] + vSeq[2]
for i in countup(3, n - 1):
  dp[i] = max(dp[i - 2], dp[i - 3]) + vSeq[i]

echo(dp[n - 1])