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 n = 0;
		
		String SArray[] = S.split("");
		String TArray[] = T.split("");
		
		for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		}
		
		System.out.println(n);
	}
} 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 n = 0;
		
		String SArray[] = S.split("");
		String TArray[] = T.split("");
		
		for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		}
		
		System.out.println(n);
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int n = 0;
		
		String SArray[] = S.split("");
		String TArray[] = T.split("");
		
		for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		}
		
		System.out.println(n);
	} main {
		Scanner in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int n = 0;
		
		String SArray[] = S.split("");
		String TArray[] = T.split("");
		
		for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		}
		
		System.out.println(n);
	} 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 n = 0; n 0 String SArray[] = S.split(""); SArray S.split("") S.split S "" String TArray[] = T.split(""); TArray T.split("") T.split T "" for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		} 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])) {
				n++;
			}
		} {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		} if(!SArray[i].equals(TArray[i])) {
				n++;
			} !SArray[i].equals(TArray[i]) SArray[i].equals(TArray[i]) SArray[i].equals SArray[i] SArray i TArray[i] TArray i {
				n++;
			} n++ n System.out.println(n) System.out.println System.out System System.out n 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 n = 0;
		
		String SArray[] = S.split("");
		String TArray[] = T.split("");
		
		for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		}
		
		System.out.println(n);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		
		String S = in.next();
		String T = in.next();
		int n = 0;
		
		String SArray[] = S.split("");
		String TArray[] = T.split("");
		
		for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		}
		
		System.out.println(n);
	}
} Main
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 n = 0;
		
		String SArray[] = S.split("");
		String TArray[] = T.split("");
		
		for(int i = 0;i < SArray.length;i++) {
			if(!SArray[i].equals(TArray[i])) {
				n++;
			}
		}
		
		System.out.println(n);
	}
}