import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		String st1 = sc.next();
		String st2 = sc.next();
		
		sc.close();
		
		int count = 0;
		
		char[] ch1 = st1.toCharArray();
		char[] ch2 = st2.toCharArray();
		
		for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		String st1 = sc.next();
		String st2 = sc.next();
		
		sc.close();
		
		int count = 0;
		
		char[] ch1 = st1.toCharArray();
		char[] ch2 = st2.toCharArray();
		
		for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		String st1 = sc.next();
		String st2 = sc.next();
		
		sc.close();
		
		int count = 0;
		
		char[] ch1 = st1.toCharArray();
		char[] ch2 = st2.toCharArray();
		
		for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		}
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
		
		String st1 = sc.next();
		String st2 = sc.next();
		
		sc.close();
		
		int count = 0;
		
		char[] ch1 = st1.toCharArray();
		char[] ch2 = st2.toCharArray();
		
		for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		}
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String st1 = sc.next(); st1 sc.next() sc.next sc String st2 = sc.next(); st2 sc.next() sc.next sc sc.close() sc.close sc int count = 0; count 0 char[] ch1 = st1.toCharArray(); ch1 st1.toCharArray() st1.toCharArray st1 char[] ch2 = st2.toCharArray(); ch2 st2.toCharArray() st2.toCharArray st2 for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < st1.length() i st1.length() st1.length st1 i++ i++ i {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		} {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		} if (ch1[i] != ch2[i]) {
				count++;
			} ch1[i] != ch2[i] ch1[i] ch1 i ch2[i] ch2 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 st1 = sc.next();
		String st2 = sc.next();
		
		sc.close();
		
		int count = 0;
		
		char[] ch1 = st1.toCharArray();
		char[] ch2 = st2.toCharArray();
		
		for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		String st1 = sc.next();
		String st2 = sc.next();
		
		sc.close();
		
		int count = 0;
		
		char[] ch1 = st1.toCharArray();
		char[] ch2 = st2.toCharArray();
		
		for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} Main
import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		String st1 = sc.next();
		String st2 = sc.next();
		
		sc.close();
		
		int count = 0;
		
		char[] ch1 = st1.toCharArray();
		char[] ch2 = st2.toCharArray();
		
		for(int i = 0; i < st1.length(); i++) {
			if (ch1[i] != ch2[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

}
