import strutils,sequtils,math
let n: int = stdin.readline.parseint
let v: seq[int] = stdin.readline.split.map(parseint)

if n != 1:
  var dp: seq[int]
  
  # initialization
  dp.add(v[0])
  
  if v[0] < v[1]:
    dp.add(v[1])
  else:
    dp.add(v[0])
  
  for i in 2..<n:
    if dp[i-2] + v[i] > dp[i-1]:
      dp.add(dp[i-2] + v[i])
    else:
      dp.add(dp[i-1])
  
  echo dp[n-1]
else:
  echo v[0]