//package  com.company;

import java.util.Scanner;

public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String s1=sc.nextLine();
        String s2=sc.nextLine();
        int n=s1.length();
        int ans=0;
        for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        }
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String s1=sc.nextLine();
        String s2=sc.nextLine();
        int n=s1.length();
        int ans=0;
        for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String s1=sc.nextLine();
        String s2=sc.nextLine();
        int n=s1.length();
        int ans=0;
        for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        }
        System.out.println(ans);
    } main {
        Scanner sc=new Scanner(System.in);
        String s1=sc.nextLine();
        String s2=sc.nextLine();
        int n=s1.length();
        int ans=0;
        for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        }
        System.out.println(ans);
    } Scanner sc=new Scanner(System.in); sc new Scanner(System.in) String s1=sc.nextLine(); s1 sc.nextLine() sc.nextLine sc String s2=sc.nextLine(); s2 sc.nextLine() sc.nextLine sc int n=s1.length(); n s1.length() s1.length s1 int ans=0; ans 0 for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        } int i=0; int i=0; i 0 i<n i n ++i ++i i {
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        } {
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        } ans+=s1.charAt(i)!=s2.charAt(i)?1:0 ans s1.charAt(i)!=s2.charAt(i)?1:0 s1.charAt(i)!=s2.charAt(i) s1.charAt(i) s1.charAt s1 i s2.charAt(i) s2.charAt s2 i 1 0 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String s1=sc.nextLine();
        String s2=sc.nextLine();
        int n=s1.length();
        int ans=0;
        for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        }
        System.out.println(ans);
    }
} public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String s1=sc.nextLine();
        String s2=sc.nextLine();
        int n=s1.length();
        int ans=0;
        for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        }
        System.out.println(ans);
    }
} Main
//package  com.company;

import java.util.Scanner;

public class Main{

    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String s1=sc.nextLine();
        String s2=sc.nextLine();
        int n=s1.length();
        int ans=0;
        for(int i=0;i<n;++i){
            ans+=s1.charAt(i)!=s2.charAt(i)?1:0;
        }
        System.out.println(ans);
    }
}