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 c = 0;
		for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		}
		System.out.println(c);
	}
} 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 c = 0;
		for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		}
		System.out.println(c);
	}
} Main public static void main(String args[]){
		Scanner	sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int c = 0;
		for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		}
		System.out.println(c);
	} main {
		Scanner	sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int c = 0;
		for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		}
		System.out.println(c);
	} 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 c = 0; c 0 for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		} int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		} {
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		} char ch1=s.charAt(i); ch1 s.charAt(i) s.charAt s i char ch2=t.charAt(i); ch2 t.charAt(i) t.charAt t i if(ch1!=ch2)
				c++; ch1!=ch2 ch1 ch2 c++ c System.out.println(c) System.out.println System.out System System.out c 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 c = 0;
		for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				c++;
		}
		System.out.println(c);
	}
}