process.stdin.setEncoding('utf-8')
process.stdin.on('data', (data) => {
    const array = data.split(/[\n]/)
    let first;
    first = [];
    const second = array[1]
    for (let character of array[0]){
        first.push(character)
    }
    let count = 0
    let res = 0
    for (let character of second){
        if (character !== first[count]){
            res ++
        }
        count ++
    }
    console.log(res)
})
