import java.util.Scanner;

public class Main {

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

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

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

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

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

} public class Main {

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

} Main
import java.util.Scanner;

public class Main {

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

}
