import java.util.Scanner;
//import java.util.Arrays;
public class Main{
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		String a = scan.next();
		String b = scan.next();
		int count = 0;
		for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		}
		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main{
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		String a = scan.next();
		String b = scan.next();
		int count = 0;
		for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		}
		System.out.println(count);
	}
} Main public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		String a = scan.next();
		String b = scan.next();
		int count = 0;
		for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		}
		System.out.println(count);
	} main {
		Scanner scan = new Scanner(System.in);
		String a = scan.next();
		String b = scan.next();
		int count = 0;
		for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		}
		System.out.println(count);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String a = scan.next(); a scan.next() scan.next scan String b = scan.next(); b scan.next() scan.next scan int count = 0; count 0 for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		} int i=0; int i=0; i 0 i<a.length() i a.length() a.length a i++ i++ i {
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		} {
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		} if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			} !a.substring(i,i+1).equals(b.substring(i,i+1)) a.substring(i,i+1).equals(b.substring(i,i+1)) a.substring(i,i+1).equals a.substring(i,i+1) a.substring a i i+1 i 1 b.substring(i,i+1) b.substring b i i+1 i 1 {
				count++;
			} 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){
		Scanner scan = new Scanner(System.in);
		String a = scan.next();
		String b = scan.next();
		int count = 0;
		for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		}
		System.out.println(count);
	}
} public class Main{
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		String a = scan.next();
		String b = scan.next();
		int count = 0;
		for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		}
		System.out.println(count);
	}
} Main
import java.util.Scanner;
//import java.util.Arrays;
public class Main{
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		String a = scan.next();
		String b = scan.next();
		int count = 0;
		for(int i=0; i<a.length(); i++){
			if(!a.substring(i,i+1).equals(b.substring(i,i+1))){
				count++;
			}
		}
		System.out.println(count);
	}
}
