import java.util.*;
public class Main{
	public static void main(String args[]){

		Scanner ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

		for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		}
		System.out.println(C);
	}
} import java.util.*; util.* java public class Main{
	public static void main(String args[]){

		Scanner ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

		for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		}
		System.out.println(C);
	}
} Main public static void main(String args[]){

		Scanner ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

		for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		}
		System.out.println(C);
	} main {

		Scanner ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

		for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		}
		System.out.println(C);
	} Scanner ob = new Scanner(System.in); ob new Scanner(System.in) String S = ob.next(); S ob.next() ob.next ob String T = ob.next(); T ob.next() ob.next ob int C = 0; C 0 for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		} int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		} {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		} if(S.charAt(i) != T.charAt(i) ){
				C++;
			} S.charAt(i) != T.charAt(i) S.charAt(i) S.charAt S i T.charAt(i) T.charAt 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 ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

		for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		}
		System.out.println(C);
	}
} public class Main{
	public static void main(String args[]){

		Scanner ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

		for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		}
		System.out.println(C);
	}
} Main
import java.util.*;
public class Main{
	public static void main(String args[]){

		Scanner ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

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