S = gets.chomp
ans = 0
stack = []
pon_cnt = 0

S.each_char do |s|
  stack << s

  if s == 'n' && stack.size >= 3
    pon_cnt += 1 if stack[-3..-1].join == 'pon'

    if stack.size >= 4 && stack[-4..-1].join == 'pain'
      if pon_cnt >= 2
        puts pon_cnt - 1
      else
        puts -1
      end
      exit
    end
  end
end

puts -1