import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		String S = stdIn.next();
		String T = stdIn.next();
		int c=0;
		for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		}
		System.out.println(c);
		stdIn.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		String S = stdIn.next();
		String T = stdIn.next();
		int c=0;
		for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		}
		System.out.println(c);
		stdIn.close();
	}
} Main public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		String S = stdIn.next();
		String T = stdIn.next();
		int c=0;
		for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		}
		System.out.println(c);
		stdIn.close();
	} main {
		Scanner stdIn = new Scanner(System.in);
		String S = stdIn.next();
		String T = stdIn.next();
		int c=0;
		for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		}
		System.out.println(c);
		stdIn.close();
	} Scanner stdIn = new Scanner(System.in); stdIn new Scanner(System.in) String S = stdIn.next(); S stdIn.next() stdIn.next stdIn String T = stdIn.next(); T stdIn.next() stdIn.next stdIn int c=0; c 0 for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		} int a=0; int a=0; a 0 a<S.length() a S.length() S.length S a++ a++ a {
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		} {
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		} if(S.charAt(a) != T.charAt(a)){
				c++;
			} S.charAt(a) != T.charAt(a) S.charAt(a) S.charAt S a T.charAt(a) T.charAt T a {
				c++;
			} c++ c System.out.println(c) System.out.println System.out System System.out c stdIn.close() stdIn.close stdIn String[] args args public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		String S = stdIn.next();
		String T = stdIn.next();
		int c=0;
		for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		}
		System.out.println(c);
		stdIn.close();
	}
} public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		String S = stdIn.next();
		String T = stdIn.next();
		int c=0;
		for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		}
		System.out.println(c);
		stdIn.close();
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		String S = stdIn.next();
		String T = stdIn.next();
		int c=0;
		for(int a=0; a<S.length(); a++){
			if(S.charAt(a) != T.charAt(a)){
				c++;
			}
		}
		System.out.println(c);
		stdIn.close();
	}
}
