import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		String s = in.next();
		String t = in.next();
		int r = 0;
		for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++;
		System.out.println(r);
	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		String s = in.next();
		String t = in.next();
		int r = 0;
		for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++;
		System.out.println(r);
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		String s = in.next();
		String t = in.next();
		int r = 0;
		for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++;
		System.out.println(r);
	} main {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		String s = in.next();
		String t = in.next();
		int r = 0;
		for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++;
		System.out.println(r);
	} Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in))); in new Scanner(new BufferedReader(new InputStreamReader(System.in))) String s = in.next(); s in.next() in.next in String t = in.next(); t in.next() in.next in int r = 0; r 0 for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++; 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))
				r++; if (s.charAt(i) != t.charAt(i))
				r++; s.charAt(i) != t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i r++ r System.out.println(r) System.out.println System.out System System.out r String[] args args public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		String s = in.next();
		String t = in.next();
		int r = 0;
		for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++;
		System.out.println(r);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		String s = in.next();
		String t = in.next();
		int r = 0;
		for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++;
		System.out.println(r);
	}
} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		String s = in.next();
		String t = in.next();
		int r = 0;
		for (int i = 0; i < s.length(); i++)
			if (s.charAt(i) != t.charAt(i))
				r++;
		System.out.println(r);
	}
}