{-# OPTIONS_GHC -Wno-unused-imports #-}
{-# OPTIONS_GHC -Wno-unused-top-binds #-}
{-# OPTIONS_GHC -Wno-missing-signatures #-}

import Control.Monad
import Control.Monad.State.Strict
import Control.Applicative
import Data.Bool
import Data.Function
import Data.List
import Data.Ord
import Data.List.Split
-- import System.IO (hFlush, stdout)
import Debug.Trace

input = getLine :: IO String
ii = readLn :: IO Int
li = map read . words <$> getLine :: IO [Int]
printYn b = putStrLn $ bool "No" "Yes" b

pairwise :: [a] -> [(a, a)]
pairwise xs = zip xs (drop 1 xs)

countIf f = length . filter f

minmax (x:xs)
  = foldl' (\(mi, ma) x -> (min mi x, max ma x)) (x, x) xs

solve ('p':'a':'i':'n':xs) k = max (k-1) (solve xs 0)
solve ('p':'o':'n':xs) k     = solve xs (k+1)
solve (_:xs) k               = solve xs k
solve [] _                   = 0

main :: IO ()
main = do
  s <- input
  let ans = solve s 0
  print $ if ans == 0 then -1 else ans