'use strict'

const main = (INPUT) => {
  const S = INPUT.split('\n')[0]
  const ary = S.split('')
  if (ary.length == [...new Set(ary)].length) {
    console.log('yes')
  } else {
    console.log('no')
  }
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'))
