import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    String s1 = scan.next(),s2=scan.next();
    int count = 0;
    for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    }
    System.out.println(""+count);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    String s1 = scan.next(),s2=scan.next();
    int count = 0;
    for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    }
    System.out.println(""+count);
  }
} Main public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    String s1 = scan.next(),s2=scan.next();
    int count = 0;
    for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    }
    System.out.println(""+count);
  } main {
    Scanner scan = new Scanner(System.in);
    String s1 = scan.next(),s2=scan.next();
    int count = 0;
    for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    }
    System.out.println(""+count);
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String s1 = scan.next() s1 scan.next() scan.next scan s2=scan.next(); s2 scan.next() scan.next scan int count = 0; count 0 for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    } int i=0; int i=0; i 0 i<s1.length() i s1.length() s1.length s1 i++ i++ i {
      if(s1.charAt(i)!=s2.charAt(i))count++;
    } {
      if(s1.charAt(i)!=s2.charAt(i))count++;
    } if(s1.charAt(i)!=s2.charAt(i))count++; s1.charAt(i)!=s2.charAt(i) s1.charAt(i) s1.charAt s1 i s2.charAt(i) s2.charAt s2 i count++ count System.out.println(""+count) System.out.println System.out System System.out ""+count "" count String[] args args public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    String s1 = scan.next(),s2=scan.next();
    int count = 0;
    for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    }
    System.out.println(""+count);
  }
} public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    String s1 = scan.next(),s2=scan.next();
    int count = 0;
    for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    }
    System.out.println(""+count);
  }
} Main
import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    String s1 = scan.next(),s2=scan.next();
    int count = 0;
    for(int i=0;i<s1.length();i++){
      if(s1.charAt(i)!=s2.charAt(i))count++;
    }
    System.out.println(""+count);
  }
}