'use strict';

const inputs = require('fs').readFileSync('/dev/stdin', 'utf8').split('\n');
const sMpI = (str) => str.split(' ').map(v => parseInt(v, 10));
const pI = v => parseInt(v, 10);

const text1 = inputs.shift().split('');
const text2 = inputs.shift().split('');

let result = 0;

for (const i in text1) {
  if (text1[i] !== text2[i]) {
    ++result;
  }
}

console.log(result);