import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = sc.next();
		String[] s1 = s.split("");
		String[] t1 = t.split("");
		
		int ans = 0;
		
		for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		}
		
		System.out.print(ans);
	}

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

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = sc.next();
		String[] s1 = s.split("");
		String[] t1 = t.split("");
		
		int ans = 0;
		
		for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		}
		
		System.out.print(ans);
	}

} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = sc.next();
		String[] s1 = s.split("");
		String[] t1 = t.split("");
		
		int ans = 0;
		
		for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		}
		
		System.out.print(ans);
	} main {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = sc.next();
		String[] s1 = s.split("");
		String[] t1 = t.split("");
		
		int ans = 0;
		
		for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		}
		
		System.out.print(ans);
	} 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 String[] s1 = s.split(""); s1 s.split("") s.split s "" String[] t1 = t.split(""); t1 t.split("") t.split t "" int ans = 0; ans 0 for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		} int i = 0; int i = 0; i 0 i < s1.length i s1.length s1 s1.length i++ i++ i {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		} {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		} if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			} s1[i].equals(t1[i]) s1[i].equals s1[i] s1 i t1[i] t1 i {
				
			} {
				ans++;
			} ans++ ans System.out.print(ans) System.out.print System.out System System.out ans String[] args args public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = sc.next();
		String[] s1 = s.split("");
		String[] t1 = t.split("");
		
		int ans = 0;
		
		for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		}
		
		System.out.print(ans);
	}

} public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = sc.next();
		String[] s1 = s.split("");
		String[] t1 = t.split("");
		
		int ans = 0;
		
		for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		}
		
		System.out.print(ans);
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		
		String s = sc.next();
		String t = sc.next();
		String[] s1 = s.split("");
		String[] t1 = t.split("");
		
		int ans = 0;
		
		for(int i = 0; i < s1.length; i++) {
			if(s1[i].equals(t1[i])) {
				
			}else {
				ans++;
			}
		}
		
		System.out.print(ans);
	}

}
