import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		try (final Scanner sc = new Scanner(System.in);) {
			final char[] s = sc.next().toCharArray();
			final char[] t = sc.next().toCharArray();

			int c=0;
			for(int i=0; i< s.length; i++) {
				if(s[i]!=t[i]) {
					c++;
				}
			}
			System.out.println(c);
		}
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		try (final Scanner sc = new Scanner(System.in);) {
			final char[] s = sc.next().toCharArray();
			final char[] t = sc.next().toCharArray();

			int c=0;
			for(int i=0; i< s.length; i++) {
				if(s[i]!=t[i]) {
					c++;
				}
			}
			System.out.println(c);
		}
	}
} Main public static void main(String[] args) {
		try (final Scanner sc = new Scanner(System.in);) {
			final char[] s = sc.next().toCharArray();
			final char[] t = sc.next().toCharArray();

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

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

			int c=0;
			for(int i=0; i< s.length; i++) {
				if(s[i]!=t[i]) {
					c++;
				}
			}
			System.out.println(c);
		} {
			final char[] s = sc.next().toCharArray();
			final char[] t = sc.next().toCharArray();

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

			int c=0;
			for(int i=0; i< s.length; i++) {
				if(s[i]!=t[i]) {
					c++;
				}
			}
			System.out.println(c);
		}
	}
} public class Main {

	public static void main(String[] args) {
		try (final Scanner sc = new Scanner(System.in);) {
			final char[] s = sc.next().toCharArray();
			final char[] t = sc.next().toCharArray();

			int c=0;
			for(int i=0; i< s.length; i++) {
				if(s[i]!=t[i]) {
					c++;
				}
			}
			System.out.println(c);
		}
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		try (final Scanner sc = new Scanner(System.in);) {
			final char[] s = sc.next().toCharArray();
			final char[] t = sc.next().toCharArray();

			int c=0;
			for(int i=0; i< s.length; i++) {
				if(s[i]!=t[i]) {
					c++;
				}
			}
			System.out.println(c);
		}
	}
}