//B
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int count = 0;
		
		for(int i = 0; i < S.length(); i++) {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		}

		System.out.println(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int count = 0;
		
		for(int i = 0; i < S.length(); i++) {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		}

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

		System.out.println(count);
	} main {
		Scanner in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int count = 0;
		
		for(int i = 0; i < S.length(); i++) {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		}

		System.out.println(count);
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) String S = in.next(); S in.next() in.next in String T = in.next(); T in.next() in.next in int count = 0; count 0 for(int i = 0; i < S.length(); i++) {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		} {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		} char s = S.charAt(i); s S.charAt(i) S.charAt S i char t = T.charAt(i); t T.charAt(i) T.charAt T i if(s != t) {
				count++;
			} s != t s t {
				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 in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int count = 0;
		
		for(int i = 0; i < S.length(); i++) {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		}

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

		System.out.println(count);
	}
} Main
//B
import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int count = 0;
		
		for(int i = 0; i < S.length(); i++) {
			char s = S.charAt(i);
			char t = T.charAt(i);
			
			if(s != t) {
				count++;
			}
		}

		System.out.println(count);
	}
}