import java.util.*;

class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String[] a = sc.next().split("",0);
		String[] b = sc.next().split("",0);
		int count = 0;
		for(int i = 0; i < a.length; i++){
			if(!a[i].equals(b[i])){
				count++;
			}
		}
		System.out.print(count);
	}
} import java.util.*; util.* java class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String[] a = sc.next().split("",0);
		String[] b = sc.next().split("",0);
		int count = 0;
		for(int i = 0; i < a.length; i++){
			if(!a[i].equals(b[i])){
				count++;
			}
		}
		System.out.print(count);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String[] a = sc.next().split("",0);
		String[] b = sc.next().split("",0);
		int count = 0;
		for(int i = 0; i < a.length; i++){
			if(!a[i].equals(b[i])){
				count++;
			}
		}
		System.out.print(count);
	} main {
		Scanner sc = new Scanner(System.in);
		String[] a = sc.next().split("",0);
		String[] b = sc.next().split("",0);
		int count = 0;
		for(int i = 0; i < a.length; i++){
			if(!a[i].equals(b[i])){
				count++;
			}
		}
		System.out.print(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String[] a = sc.next().split("",0); a sc.next().split("",0) sc.next().split sc.next() sc.next sc "" 0 String[] b = sc.next().split("",0); b sc.next().split("",0) sc.next().split sc.next() sc.next sc "" 0 int count = 0; count 0 for(int i = 0; i < a.length; i++){
			if(!a[i].equals(b[i])){
				count++;
			}
		} int i = 0; int i = 0; i 0 i < a.length i a.length a a.length i++ i++ i {
			if(!a[i].equals(b[i])){
				count++;
			}
		} {
			if(!a[i].equals(b[i])){
				count++;
			}
		} if(!a[i].equals(b[i])){
				count++;
			} !a[i].equals(b[i]) a[i].equals(b[i]) a[i].equals a[i] a i b[i] b i {
				count++;
			} count++ count System.out.print(count) System.out.print System.out System System.out count String[] args args
import java.util.*;

class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String[] a = sc.next().split("",0);
		String[] b = sc.next().split("",0);
		int count = 0;
		for(int i = 0; i < a.length; i++){
			if(!a[i].equals(b[i])){
				count++;
			}
		}
		System.out.print(count);
	}
}