import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int cn = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		}
		System.out.println(cn);
		sc.close();
	}

} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int cn = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		}
		System.out.println(cn);
		sc.close();
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int cn = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		}
		System.out.println(cn);
		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int cn = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		}
		System.out.println(cn);
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc String t = sc.next(); t sc.next() sc.next sc int cn = 0; cn 0 for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

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

			} else {
				cn++;
			}

		} {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		} if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			} s.substring(i, i + 1).equals(t.substring(i, i + 1)) s.substring(i, i + 1).equals s.substring(i, i + 1) s.substring s i i + 1 i 1 t.substring(i, i + 1) t.substring t i i + 1 i 1 {

			} {
				cn++;
			} cn++ cn System.out.println(cn) System.out.println System.out System System.out cn sc.close() sc.close sc String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int cn = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		}
		System.out.println(cn);
		sc.close();
	}

} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int cn = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		}
		System.out.println(cn);
		sc.close();
	}

} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int cn = 0;
		for (int i = 0; i < s.length(); i++) {
			if (s.substring(i, i + 1).equals(t.substring(i, i + 1))) {

			} else {
				cn++;
			}

		}
		System.out.println(cn);
		sc.close();
	}

}