	import java.util.*;
	import java.util.Map.Entry;
	 
	 
	 class Main {
		 static int mod =  (int) (Math.pow(10,9)+7);
//		 static int mod =  (int) 998244353;
		 static List<ArrayList<Integer>> list= new ArrayList<ArrayList<Integer>>();
		 public static void main(String[] args) {
	    	
	        Scanner sc = new Scanner(System.in);

	        String S = sc.next();
	        char[] s = S.toCharArray();
	        String T = sc.next();
	        char[] t = T.toCharArray();
	        int cnt=0;
	        for(int i=0;i<s.length;i++) {
	        	if(s[i]!=t[i])cnt++;
	        }
	        System.out.println(cnt);
		 }
	} import java.util.*; util.* java import java.util.Map.Entry; Entry java.util.Map class Main {
		 static int mod =  (int) (Math.pow(10,9)+7);
//		 static int mod =  (int) 998244353;
		 static List<ArrayList<Integer>> list= new ArrayList<ArrayList<Integer>>();
		 public static void main(String[] args) {
	    	
	        Scanner sc = new Scanner(System.in);

	        String S = sc.next();
	        char[] s = S.toCharArray();
	        String T = sc.next();
	        char[] t = T.toCharArray();
	        int cnt=0;
	        for(int i=0;i<s.length;i++) {
	        	if(s[i]!=t[i])cnt++;
	        }
	        System.out.println(cnt);
		 }
	} Main static int mod =  (int) (Math.pow(10,9)+7); mod (int) (Math.pow(10,9)+7) Math.pow(10,9) Math.pow Math 10 9 7 //		 static int mod =  (int) 998244353;
		 static List<ArrayList<Integer>> list= new ArrayList<ArrayList<Integer>>(); list new ArrayList<ArrayList<Integer>>() public static void main(String[] args) {
	    	
	        Scanner sc = new Scanner(System.in);

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

	        String S = sc.next();
	        char[] s = S.toCharArray();
	        String T = sc.next();
	        char[] t = T.toCharArray();
	        int cnt=0;
	        for(int i=0;i<s.length;i++) {
	        	if(s[i]!=t[i])cnt++;
	        }
	        System.out.println(cnt);
		 } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.next(); S sc.next() sc.next sc char[] s = S.toCharArray(); s S.toCharArray() S.toCharArray S String T = sc.next(); T sc.next() sc.next sc char[] t = T.toCharArray(); t T.toCharArray() T.toCharArray T int cnt=0; cnt 0 for(int i=0;i<s.length;i++) {
	        	if(s[i]!=t[i])cnt++;
	        } int i=0; int i=0; i 0 i<s.length i s.length s s.length i++ i++ i {
	        	if(s[i]!=t[i])cnt++;
	        } {
	        	if(s[i]!=t[i])cnt++;
	        } if(s[i]!=t[i])cnt++; s[i]!=t[i] s[i] s i t[i] t i cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args
	import java.util.*;
	import java.util.Map.Entry;
	 
	 
	 class Main {
		 static int mod =  (int) (Math.pow(10,9)+7);
//		 static int mod =  (int) 998244353;
		 static List<ArrayList<Integer>> list= new ArrayList<ArrayList<Integer>>();
		 public static void main(String[] args) {
	    	
	        Scanner sc = new Scanner(System.in);

	        String S = sc.next();
	        char[] s = S.toCharArray();
	        String T = sc.next();
	        char[] t = T.toCharArray();
	        int cnt=0;
	        for(int i=0;i<s.length;i++) {
	        	if(s[i]!=t[i])cnt++;
	        }
	        System.out.println(cnt);
		 }
	}