process.stdin.resume();
process.stdin.setEncoding("utf8");
process.stdin.on("data", input => {
  const splited = input.split("\n");
  const S = Array.from(splited[0]);
  const T = Array.from(splited[1]);
  let count = 0;
  S.forEach((value, index) => {
    if(value !== T[index]) {
      count++;
    }
  })
  console.log(count);
});
