const main = async () => {
  'use strict'
  const input = require('fs').readFileSync('/dev/stdin', 'UTF-8').trim()
  
  let setting = input.split('\n')
  
  const str = setting[0].split('')
  const sample = setting[1].split('')

  let count = 0

  for (let i = 0; i < str.length; i++) {
    if (str[i] !== sample[i]) {
      count++
    }
  }

  console.log(count)
}

main()