import java.util.*;

import javax.lang.model.util.ElementScanner6;
 
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		}
		System.out.println(count);

	}
} import java.util.*; util.* java import javax.lang.model.util.ElementScanner6; ElementScanner6 javax.lang.model.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		}
		System.out.println(count);

	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		}
		System.out.println(count);

	} main {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		}
		System.out.println(count);

	} 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 count = 0; count 0 for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		} int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i ++ i ++ i {
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		} {
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		} char s = S.charAt(i); s S.charAt(i) S.charAt S i char t = T.charAt(i); t T.charAt(i) T.charAt T i if(s != t)
			count ++; s != t s t 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 sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		}
		System.out.println(count);

	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		}
		System.out.println(count);

	}
} Main
import java.util.*;

import javax.lang.model.util.ElementScanner6;
 
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int count = 0;

		for(int i = 0; i < S.length(); i ++){
			char s = S.charAt(i);
			char t = T.charAt(i);
			if(s != t)
			count ++;
		}
		System.out.println(count);

	}
}