process.stdin.setEncoding('utf-8')
process.stdin.on('data', (data) => {
    const array = data.trim().split(/[\n]/)
    let res = 0
    if(1 <= array[0].length <= 200000){
        for (let i = 0; i < array[0].length; i++) {
            if (array[0][i] !== array[1][i]){
                res ++
            }
        }
        console.log(res)
    }
})
