import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		String N = scan.next();
		String T = scan.next();
		String[] n = N.split("");
		String[] t = T.split("");
		int c =0;
		
		for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		}
		System.out.println(c);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		String N = scan.next();
		String T = scan.next();
		String[] n = N.split("");
		String[] t = T.split("");
		int c =0;
		
		for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		}
		System.out.println(c);
	}
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		String N = scan.next();
		String T = scan.next();
		String[] n = N.split("");
		String[] t = T.split("");
		int c =0;
		
		for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		}
		System.out.println(c);
	} main {
		Scanner scan = new Scanner(System.in);
		
		String N = scan.next();
		String T = scan.next();
		String[] n = N.split("");
		String[] t = T.split("");
		int c =0;
		
		for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		}
		System.out.println(c);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String N = scan.next(); N scan.next() scan.next scan String T = scan.next(); T scan.next() scan.next scan String[] n = N.split(""); n N.split("") N.split N "" String[] t = T.split(""); t T.split("") T.split T "" int c =0; c 0 for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		} int i=0; int i=0; i 0 i<N.length() i N.length() N.length N i++ i++ i {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		} {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		} if(n[i].equals(t[i])){
			}else {
				c++;
			} n[i].equals(t[i]) n[i].equals n[i] n i t[i] t i {
			} {
				c++;
			} c++ c System.out.println(c) System.out.println System.out System System.out c String[] args args public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		String N = scan.next();
		String T = scan.next();
		String[] n = N.split("");
		String[] t = T.split("");
		int c =0;
		
		for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		}
		System.out.println(c);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		String N = scan.next();
		String T = scan.next();
		String[] n = N.split("");
		String[] t = T.split("");
		int c =0;
		
		for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		}
		System.out.println(c);
	}
} Main
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		
		String N = scan.next();
		String T = scan.next();
		String[] n = N.split("");
		String[] t = T.split("");
		int c =0;
		
		for(int i=0; i<N.length(); i++) {
			if(n[i].equals(t[i])){
			}else {
				c++;
			}
		}
		System.out.println(c);
	}
}
