const processData = (lines) => {
  const a = lines[0]
  const b = lines[1]
  let counter = 0
  for (let i=0; i<a.length; i++) {
    if (a[i] !== b[i]) {
      counter++
    }
  }
  console.log(counter)
}

let i = ''
process.stdin.on('data', c => i += c)
process.stdin.on('end', () => {
  const {EOL} = require('os')
  const lines = i.split(EOL) /*your input text, split by lines*/
  processData(lines)
})
