
import java.util.*;

public class Main
{

    private final static int MOD = 1_000_000_007;

    public static int gcd(int a, int b) { 
        // Everything divides 0  
        if (a == 0) 
          return b; 
        if (b == 0) 
          return a; 
       
        // base case 
        if (a == b) 
            return a; 
       
        // a is greater 
        if (a > b) 
            return gcd(a-b, b); 
        return gcd(a, b-a); 
    }
    
    public static long mod(long a, long b) {
        return ((a % b) + b ) % b;
    }

    public static int mod (int a, int b) {
        return ((a % b) + b ) % b;
    }
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
	String s = in.nextLine();
	String t = in.nextLine();
	int res = 0;
	for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	}
	System.out.println(res);
	in.close();
    }
} import java.util.*; util.* java public class Main
{

    private final static int MOD = 1_000_000_007;

    public static int gcd(int a, int b) { 
        // Everything divides 0  
        if (a == 0) 
          return b; 
        if (b == 0) 
          return a; 
       
        // base case 
        if (a == b) 
            return a; 
       
        // a is greater 
        if (a > b) 
            return gcd(a-b, b); 
        return gcd(a, b-a); 
    }
    
    public static long mod(long a, long b) {
        return ((a % b) + b ) % b;
    }

    public static int mod (int a, int b) {
        return ((a % b) + b ) % b;
    }
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
	String s = in.nextLine();
	String t = in.nextLine();
	int res = 0;
	for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	}
	System.out.println(res);
	in.close();
    }
} Main private final static int MOD = 1_000_000_007; MOD 1_000_000_007 public static int gcd(int a, int b) { 
        // Everything divides 0  
        if (a == 0) 
          return b; 
        if (b == 0) 
          return a; 
       
        // base case 
        if (a == b) 
            return a; 
       
        // a is greater 
        if (a > b) 
            return gcd(a-b, b); 
        return gcd(a, b-a); 
    } gcd { 
        // Everything divides 0  
        if (a == 0) 
          return b; 
        if (b == 0) 
          return a; 
       
        // base case 
        if (a == b) 
            return a; 
       
        // a is greater 
        if (a > b) 
            return gcd(a-b, b); 
        return gcd(a, b-a); 
    } if (a == 0) 
          return b; a == 0 a 0 return b; b if (b == 0) 
          return a; b == 0 b 0 return a; a if (a == b) 
            return a; a == b a b return a; a if (a > b) 
            return gcd(a-b, b); a > b a b return gcd(a-b, b); gcd(a-b, b) gcd a-b a b b return gcd(a, b-a); gcd(a, b-a) gcd a b-a b a int a a int b b public static long mod(long a, long b) {
        return ((a % b) + b ) % b;
    } mod {
        return ((a % b) + b ) % b;
    } return ((a % b) + b ) % b; ((a % b) + b ) % b ((a % b) + b ) (a % b) a b b b long a a long b b public static int mod (int a, int b) {
        return ((a % b) + b ) % b;
    } mod {
        return ((a % b) + b ) % b;
    } return ((a % b) + b ) % b; ((a % b) + b ) % b ((a % b) + b ) (a % b) a b b b int a a int b b public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
	String s = in.nextLine();
	String t = in.nextLine();
	int res = 0;
	for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	}
	System.out.println(res);
	in.close();
    } main {
        Scanner in = new Scanner(System.in);
	String s = in.nextLine();
	String t = in.nextLine();
	int res = 0;
	for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	}
	System.out.println(res);
	in.close();
    } Scanner in = new Scanner(System.in); in new Scanner(System.in) String s = in.nextLine(); s in.nextLine() in.nextLine in String t = in.nextLine(); t in.nextLine() in.nextLine in int res = 0; res 0 for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	} int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
	    if (s.charAt(i) != t.charAt(i)) res++;
	} {
	    if (s.charAt(i) != t.charAt(i)) res++;
	} if (s.charAt(i) != t.charAt(i)) res++; s.charAt(i) != t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i res++ res System.out.println(res) System.out.println System.out System System.out res in.close() in.close in String[] args args public class Main
{

    private final static int MOD = 1_000_000_007;

    public static int gcd(int a, int b) { 
        // Everything divides 0  
        if (a == 0) 
          return b; 
        if (b == 0) 
          return a; 
       
        // base case 
        if (a == b) 
            return a; 
       
        // a is greater 
        if (a > b) 
            return gcd(a-b, b); 
        return gcd(a, b-a); 
    }
    
    public static long mod(long a, long b) {
        return ((a % b) + b ) % b;
    }

    public static int mod (int a, int b) {
        return ((a % b) + b ) % b;
    }
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
	String s = in.nextLine();
	String t = in.nextLine();
	int res = 0;
	for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	}
	System.out.println(res);
	in.close();
    }
} public class Main
{

    private final static int MOD = 1_000_000_007;

    public static int gcd(int a, int b) { 
        // Everything divides 0  
        if (a == 0) 
          return b; 
        if (b == 0) 
          return a; 
       
        // base case 
        if (a == b) 
            return a; 
       
        // a is greater 
        if (a > b) 
            return gcd(a-b, b); 
        return gcd(a, b-a); 
    }
    
    public static long mod(long a, long b) {
        return ((a % b) + b ) % b;
    }

    public static int mod (int a, int b) {
        return ((a % b) + b ) % b;
    }
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
	String s = in.nextLine();
	String t = in.nextLine();
	int res = 0;
	for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	}
	System.out.println(res);
	in.close();
    }
} Main

import java.util.*;

public class Main
{

    private final static int MOD = 1_000_000_007;

    public static int gcd(int a, int b) { 
        // Everything divides 0  
        if (a == 0) 
          return b; 
        if (b == 0) 
          return a; 
       
        // base case 
        if (a == b) 
            return a; 
       
        // a is greater 
        if (a > b) 
            return gcd(a-b, b); 
        return gcd(a, b-a); 
    }
    
    public static long mod(long a, long b) {
        return ((a % b) + b ) % b;
    }

    public static int mod (int a, int b) {
        return ((a % b) + b ) % b;
    }
    
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
	String s = in.nextLine();
	String t = in.nextLine();
	int res = 0;
	for (int i = 0; i < s.length(); i++) {
	    if (s.charAt(i) != t.charAt(i)) res++;
	}
	System.out.println(res);
	in.close();
    }
}
