import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String S = scan.next();
		String T = scan.next();
		scan.close();

		String[] sArray = S.split("");
		String[] tArray = T.split("");

		int count = 0;
		for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		}
		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String S = scan.next();
		String T = scan.next();
		scan.close();

		String[] sArray = S.split("");
		String[] tArray = T.split("");

		int count = 0;
		for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		}
		System.out.println(count);
	}
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String S = scan.next();
		String T = scan.next();
		scan.close();

		String[] sArray = S.split("");
		String[] tArray = T.split("");

		int count = 0;
		for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		}
		System.out.println(count);
	} main {
		Scanner scan = new Scanner(System.in);
		String S = scan.next();
		String T = scan.next();
		scan.close();

		String[] sArray = S.split("");
		String[] tArray = T.split("");

		int count = 0;
		for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		}
		System.out.println(count);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String S = scan.next(); S scan.next() scan.next scan String T = scan.next(); T scan.next() scan.next scan scan.close() scan.close scan String[] sArray = S.split(""); sArray S.split("") S.split S "" String[] tArray = T.split(""); tArray T.split("") T.split T "" int count = 0; count 0 for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		} int i = 0; int i = 0; i 0 i < sArray.length i sArray.length sArray sArray.length i++ i++ i {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		} {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		} if (!sArray[i].equals(tArray[i])) {
				count += 1;
			} !sArray[i].equals(tArray[i]) sArray[i].equals(tArray[i]) sArray[i].equals sArray[i] sArray i tArray[i] tArray i {
				count += 1;
			} count += 1 count 1 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 scan = new Scanner(System.in);
		String S = scan.next();
		String T = scan.next();
		scan.close();

		String[] sArray = S.split("");
		String[] tArray = T.split("");

		int count = 0;
		for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		}
		System.out.println(count);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String S = scan.next();
		String T = scan.next();
		scan.close();

		String[] sArray = S.split("");
		String[] tArray = T.split("");

		int count = 0;
		for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		}
		System.out.println(count);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		String S = scan.next();
		String T = scan.next();
		scan.close();

		String[] sArray = S.split("");
		String[] tArray = T.split("");

		int count = 0;
		for (int i = 0; i < sArray.length; i++) {
			if (!sArray[i].equals(tArray[i])) {
				count += 1;
			}
		}
		System.out.println(count);
	}
}