function Main(arg) {
  let [s, t] = arg.trim().split('\n');
  let count = 0;
  if(s != t){
    for(i = 0; i < s.length; i++){
      const size = s.length > i+1 ? i+1 : s.length;
      if (s.substring(i, size) != t.substring(i, size) ){
        count++;
      }
    }
  }
  console.log(count);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));