import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);

		String T = sc.next();
		String S = sc.next();
      
		StringBuilder t = new StringBuilder();
		StringBuilder s = new StringBuilder();

		t.append(T);
		s.append(S);

		int count = 0;

		for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.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 sc = new Scanner(System.in);

		String T = sc.next();
		String S = sc.next();
      
		StringBuilder t = new StringBuilder();
		StringBuilder s = new StringBuilder();

		t.append(T);
		s.append(S);

		int count = 0;

		for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		}

		System.out.println(count);

	}

} Main public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);

		String T = sc.next();
		String S = sc.next();
      
		StringBuilder t = new StringBuilder();
		StringBuilder s = new StringBuilder();

		t.append(T);
		s.append(S);

		int count = 0;

		for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		}

		System.out.println(count);

	} main {
    	Scanner sc = new Scanner(System.in);

		String T = sc.next();
		String S = sc.next();
      
		StringBuilder t = new StringBuilder();
		StringBuilder s = new StringBuilder();

		t.append(T);
		s.append(S);

		int count = 0;

		for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		}

		System.out.println(count);

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String T = sc.next(); T sc.next() sc.next sc String S = sc.next(); S sc.next() sc.next sc StringBuilder t = new StringBuilder(); t new StringBuilder() StringBuilder s = new StringBuilder(); s new StringBuilder() t.append(T) t.append t T s.append(S) s.append s S int count = 0; count 0 for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		} int i=0; int i=0; i 0 i<t.length() i t.length() t.length t i++ i++ i {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		} {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		} if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++; !t.substring(i,i+1).equals(s.substring(i, i+1)) t.substring(i,i+1).equals(s.substring(i, i+1)) t.substring(i,i+1).equals t.substring(i,i+1) t.substring t i i+1 i 1 s.substring(i, i+1) s.substring s i i+1 i 1 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 T = sc.next();
		String S = sc.next();
      
		StringBuilder t = new StringBuilder();
		StringBuilder s = new StringBuilder();

		t.append(T);
		s.append(S);

		int count = 0;

		for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		}

		System.out.println(count);

	}

} public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);

		String T = sc.next();
		String S = sc.next();
      
		StringBuilder t = new StringBuilder();
		StringBuilder s = new StringBuilder();

		t.append(T);
		s.append(S);

		int count = 0;

		for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		}

		System.out.println(count);

	}

} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);

		String T = sc.next();
		String S = sc.next();
      
		StringBuilder t = new StringBuilder();
		StringBuilder s = new StringBuilder();

		t.append(T);
		s.append(S);

		int count = 0;

		for(int i=0;i<t.length();i++) {      
			if(!t.substring(i,i+1).equals(s.substring(i, i+1))) count++;
		}

		System.out.println(count);

	}

}