import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String s=scan.nextLine();
		String t=scan.nextLine();
		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.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String s=scan.nextLine();
		String t=scan.nextLine();
		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 scan = new Scanner(System.in);
		String s=scan.nextLine();
		String t=scan.nextLine();
		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 scan = new Scanner(System.in);
		String s=scan.nextLine();
		String t=scan.nextLine();
		int c=0;
		for (int i=0;i<s.length();i++) {
			if(s.charAt(i)!=t.charAt(i))c++;
		}
		System.out.println(c);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String s=scan.nextLine(); s scan.nextLine() scan.nextLine scan String t=scan.nextLine(); t scan.nextLine() scan.nextLine scan 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 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 s=scan.nextLine();
		String t=scan.nextLine();
		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 scan = new Scanner(System.in);
		String s=scan.nextLine();
		String t=scan.nextLine();
		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.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String s=scan.nextLine();
		String t=scan.nextLine();
		int c=0;
		for (int i=0;i<s.length();i++) {
			if(s.charAt(i)!=t.charAt(i))c++;
		}
		System.out.println(c);
	}

}
