function Main(input) {
    input = input.split("\n");
    const preWords = input[0].split('');
    const nextWords = input[1].split('');
    
    let num = 0;

    if (input[0] === input[1]) {
        console.log(0);
    } else {
        for (let i = 0; i < preWords.length; i++) {
            if (preWords[i] !== nextWords[i]) {
                num ++;        
            }
        }
         console.log(num);
    }

}