import java.util.*;

class Main{
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int diff = 0;
		
		String[] ss = s.split("");
		String[] tt = t.split("");
		
		for(int i=0;i<ss.length;i++) {
			if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			}
		}
		
		System.out.println(diff);

	}
} import java.util.*; util.* java class Main{
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int diff = 0;
		
		String[] ss = s.split("");
		String[] tt = t.split("");
		
		for(int i=0;i<ss.length;i++) {
			if(ss[i].equals(tt[i])) {
			}else {
				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();
		int diff = 0;
		
		String[] ss = s.split("");
		String[] tt = t.split("");
		
		for(int i=0;i<ss.length;i++) {
			if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			}
		}
		
		System.out.println(diff);

	} main {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int diff = 0;
		
		String[] ss = s.split("");
		String[] tt = t.split("");
		
		for(int i=0;i<ss.length;i++) {
			if(ss[i].equals(tt[i])) {
			}else {
				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 int diff = 0; diff 0 String[] ss = s.split(""); ss s.split("") s.split s "" String[] tt = t.split(""); tt t.split("") t.split t "" for(int i=0;i<ss.length;i++) {
			if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			}
		} int i=0; int i=0; i 0 i<ss.length i ss.length ss ss.length i++ i++ i {
			if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			}
		} {
			if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			}
		} if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			} ss[i].equals(tt[i]) ss[i].equals ss[i] ss i tt[i] tt i {
			} {
				diff++;
			} diff++ diff System.out.println(diff) System.out.println System.out System System.out diff String args[] args
import java.util.*;

class Main{
	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int diff = 0;
		
		String[] ss = s.split("");
		String[] tt = t.split("");
		
		for(int i=0;i<ss.length;i++) {
			if(ss[i].equals(tt[i])) {
			}else {
				diff++;
			}
		}
		
		System.out.println(diff);

	}
}