import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int c = 0;
		char[] s = sc.next().toCharArray();
		char[] t = sc.next().toCharArray();

		for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		}

		System.out.println(c);
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int c = 0;
		char[] s = sc.next().toCharArray();
		char[] t = sc.next().toCharArray();

		for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		}

		System.out.println(c);
	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int c = 0;
		char[] s = sc.next().toCharArray();
		char[] t = sc.next().toCharArray();

		for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		}

		System.out.println(c);
	} main {

		Scanner sc = new Scanner(System.in);

		int c = 0;
		char[] s = sc.next().toCharArray();
		char[] t = sc.next().toCharArray();

		for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		}

		System.out.println(c);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int c = 0; c 0 char[] s = sc.next().toCharArray(); s sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc char[] t = sc.next().toCharArray(); t sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		} int i = 0; int i = 0; i 0 i < s.length i s.length s s.length i++ i++ i {
			c += s[i] != t[i] ? 1 : 0;
		} {
			c += s[i] != t[i] ? 1 : 0;
		} c += s[i] != t[i] ? 1 : 0 c s[i] != t[i] ? 1 : 0 s[i] != t[i] s[i] s i t[i] t i 1 0 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 sc = new Scanner(System.in);

		int c = 0;
		char[] s = sc.next().toCharArray();
		char[] t = sc.next().toCharArray();

		for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		}

		System.out.println(c);
	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int c = 0;
		char[] s = sc.next().toCharArray();
		char[] t = sc.next().toCharArray();

		for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		}

		System.out.println(c);
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int c = 0;
		char[] s = sc.next().toCharArray();
		char[] t = sc.next().toCharArray();

		for(int i = 0; i < s.length; i++) {
			c += s[i] != t[i] ? 1 : 0;
		}

		System.out.println(c);
	}
}