import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n=0;
		String str1 = in.next();
		String str2 = in.next();
		for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		}
		System.out.print(n);
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n=0;
		String str1 = in.next();
		String str2 = in.next();
		for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		}
		System.out.print(n);
	}

} Main public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n=0;
		String str1 = in.next();
		String str2 = in.next();
		for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		}
		System.out.print(n);
	} main {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n=0;
		String str1 = in.next();
		String str2 = in.next();
		for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		}
		System.out.print(n);
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int n=0; n 0 String str1 = in.next(); str1 in.next() in.next in String str2 = in.next(); str2 in.next() in.next in for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		} int i=0; int i=0; i 0 i<str1.length() i str1.length() str1.length str1 i++ i++ i {
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		} {
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		} if(str1.charAt(i) != str2.charAt(i))
				n++; str1.charAt(i) != str2.charAt(i) str1.charAt(i) str1.charAt str1 i str2.charAt(i) str2.charAt str2 i n++ n System.out.print(n) System.out.print System.out System System.out n String[] args args public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n=0;
		String str1 = in.next();
		String str2 = in.next();
		for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		}
		System.out.print(n);
	}

} public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n=0;
		String str1 = in.next();
		String str2 = in.next();
		for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		}
		System.out.print(n);
	}

} Main
import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner in = new Scanner(System.in);
		int n=0;
		String str1 = in.next();
		String str2 = in.next();
		for(int i=0;i<str1.length();i++)
		{
			if(str1.charAt(i) != str2.charAt(i))
				n++;
		}
		System.out.print(n);
	}

}
