using System;
using System.Numerics;
using System.Linq;
using System.Collections.Generic;
using System.Text;
using System.Collections;

namespace debug
{
    class main
    {
        static void Main(string[] args)
        {
            //問題クラスを展開
            ProgramB a = new ProgramB();
            a.main();//実行する

        }

    }
    //ABC170
    class ProgramA
    {
        public void main()
        {
            //入力
            int a = int.Parse(Console.ReadLine());

            //入力が0ならその位置を答で出す
            Console.WriteLine(a + a*a + a*a*a);

        }
    }

    class ProgramB
    {
        public void main()
        {
            //入力
            string s = Console.ReadLine();
            string t = Console.ReadLine();

            int count = 0;

            for (int i = 0; i < s.Length; i++)
            {
                if (s[i] != t[i])
                    count++;
            }

            Console.WriteLine(count);


        }
    }

    class ProgramC
    {
        public void main()
        {

            //入力
            long n = long.Parse(Console.ReadLine());
            long n2 = n;

            List<long> list = new List<long>();
            long count = 0;
            long t = 100;

            while (n2 != 0)
            {
                list.Add(n2 % 26);
                n2 /= 26;
            }

            for (int i = 0; i < list.Count; i++)
            {
                if (i == list.Count - 1)
                    Console.WriteLine((char)(list[list.Count - 1 - i] + 'a' -1));
                else
                    Console.Write((char)(list[list.Count - 1 - i] + 'a'));
              
            }

        }
    }

    class ProgramD
    {
        public void main()
        {

            //入力
            long n = long.Parse(Console.ReadLine());
            string[] s = Console.ReadLine().Split(' ');
            long[] a = new long[100000];


            for (int i = 0; i < n; i++)
                a[long.Parse(s[i]) -1]++;

            long sum = 0;

            for (int i = 0; i < n; i++)
                sum += long.Parse(s[i]);

            long q = long.Parse(Console.ReadLine());


            //それぞれの数で残るか検討
            for (int i = 0; i < q; i++)
            {
                string[] t = Console.ReadLine().Split(' ');
                sum -= a[long.Parse(t[0]) - 1] * long.Parse(t[0]);
                sum += a[long.Parse(t[0]) - 1] * long.Parse(t[1]);
                a[long.Parse(t[1]) - 1] += a[long.Parse(t[0]) -1];
                a[long.Parse(t[0]) - 1] = 0;
                //答え出力
                Console.WriteLine(sum);


            }

           
        }
    }

    class ProgramE
    {

        public void main()
        {
            //入力
            int n = int.Parse(Console.ReadLine());
            string[] s = Console.ReadLine().Split(' ');
            long[] a = new long[n];

            for (int i = 0; i < n; i++)
                a[i] = long.Parse(s[i]);

            long sum = a[0] ^ a[1];

            for (int i = 2; i < n; i++)
                sum = sum ^ a[i];

            for (int i = 0; i < n; i++)
                Console.Write((sum ^ a[i]) + " ");

            
        }

        
    }
 
}






Measured memory_bytes: 27528