import java.util.*;
public class Main{
	public static void main(String[] args){
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	}
} import java.util.*; util.* java public class Main{
	public static void main(String[] args){
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	}
} Main public static void main(String[] args){
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	} main {
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	} Main obj=new Main(); obj new Main() Scanner sc=new Scanner(System.in); sc new Scanner(System.in) String s=sc.next(); s sc.next() sc.next sc String t=sc.next(); t sc.next() sc.next sc int n=s.length() n s.length() s.length s count=0; count 0 for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			if(s.charAt(i)!=t.charAt(i))
				count++;
		} {
			if(s.charAt(i)!=t.charAt(i))
				count++;
		} if(s.charAt(i)!=t.charAt(i))
				count++; s.charAt(i)!=t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main{
	public static void main(String[] args){
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	}
} public class Main{
	public static void main(String[] args){
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	}
} Main
import java.util.*;
public class Main{
	public static void main(String[] args){
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	}
}