import java.util.Scanner;
import java.util.regex.Pattern;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		}
		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util import java.util.regex.Pattern; Pattern java.util.regex public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		}
		System.out.println(count);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		}
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		String[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		}
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] s = sc.nextLine().split(""); s sc.nextLine().split("") sc.nextLine().split sc.nextLine() sc.nextLine sc "" String[] t = sc.nextLine().split(""); t sc.nextLine().split("") sc.nextLine().split sc.nextLine() sc.nextLine sc "" sc.close() sc.close sc int size = s.length; size s.length s s.length int count = 0; count 0 for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < size i size i++ i++ i {
			if (!s[i].equals(t[i])) {
				count++;
			}
		} {
			if (!s[i].equals(t[i])) {
				count++;
			}
		} if (!s[i].equals(t[i])) {
				count++;
			} !s[i].equals(t[i]) s[i].equals(t[i]) s[i].equals s[i] s i t[i] t i {
				count++;
			} 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[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		}
		System.out.println(count);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		}
		System.out.println(count);
	}
} Main
import java.util.Scanner;
import java.util.regex.Pattern;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String[] s = sc.nextLine().split("");
		String[] t = sc.nextLine().split("");
		sc.close();
		int size = s.length;
		int count = 0;
		for (int i = 0; i < size; i++) {
			if (!s[i].equals(t[i])) {
				count++;
			}
		}
		System.out.println(count);
	}
}
