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