import java.io.*;
public class Main
{
	public static void main(String[] args) throws IOException
	{
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String s= br.readLine();
	    String t=br.readLine();
	    int count=0;
	    for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    }
	   System.out.println(count);

	   }
} import java.io.*; io.* java public class Main
{
	public static void main(String[] args) throws IOException
	{
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String s= br.readLine();
	    String t=br.readLine();
	    int count=0;
	    for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    }
	   System.out.println(count);

	   }
} Main public static void main(String[] args) throws IOException
	{
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String s= br.readLine();
	    String t=br.readLine();
	    int count=0;
	    for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    }
	   System.out.println(count);

	   } main {
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String s= br.readLine();
	    String t=br.readLine();
	    int count=0;
	    for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    }
	   System.out.println(count);

	   } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) String s= br.readLine(); s br.readLine() br.readLine br String t=br.readLine(); t br.readLine() br.readLine br int count=0; count 0 for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    } 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)) continue;
	        else count++;
	    } {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    } if(s.charAt(i)==t.charAt(i)) continue;
	        else count++; s.charAt(i)==t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i continue; count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main
{
	public static void main(String[] args) throws IOException
	{
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String s= br.readLine();
	    String t=br.readLine();
	    int count=0;
	    for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    }
	   System.out.println(count);

	   }
} public class Main
{
	public static void main(String[] args) throws IOException
	{
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String s= br.readLine();
	    String t=br.readLine();
	    int count=0;
	    for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    }
	   System.out.println(count);

	   }
} Main
import java.io.*;
public class Main
{
	public static void main(String[] args) throws IOException
	{
	    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	    String s= br.readLine();
	    String t=br.readLine();
	    int count=0;
	    for(int i=0;i<s.length();i++)
	    {
	        if(s.charAt(i)==t.charAt(i)) continue;
	        else count++;
	    }
	   System.out.println(count);

	   }
}
