console.log((args=>{
  const [S,T] = args.trim().split('\n');
  let c = 0;
  for ( let i = 0, l = S.length; i < l; i++ ) {
    if ( S[i] !== T[i] ) c++;
  }
  return `${c}`;
})(require('fs').readFileSync('/dev/stdin', 'utf8')));
