import java.util.Scanner;

public class Main{
  public static void main(String args[]){
    Scanner scanner = new Scanner(System.in);
    String S = scanner.next();
    String T = scanner.next();
    int count = 0;
    for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    }
    System.out.println(count);
  }
} import java.util.Scanner; Scanner java.util public class Main{
  public static void main(String args[]){
    Scanner scanner = new Scanner(System.in);
    String S = scanner.next();
    String T = scanner.next();
    int count = 0;
    for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    }
    System.out.println(count);
  }
} Main public static void main(String args[]){
    Scanner scanner = new Scanner(System.in);
    String S = scanner.next();
    String T = scanner.next();
    int count = 0;
    for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    }
    System.out.println(count);
  } main {
    Scanner scanner = new Scanner(System.in);
    String S = scanner.next();
    String T = scanner.next();
    int count = 0;
    for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    }
    System.out.println(count);
  } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) String S = scanner.next(); S scanner.next() scanner.next scanner String T = scanner.next(); T scanner.next() scanner.next scanner int count = 0; count 0 for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      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;
      count++;
    } {
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    } if(S.charAt(i) == T.charAt(i)) continue; 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[]){
    Scanner scanner = new Scanner(System.in);
    String S = scanner.next();
    String T = scanner.next();
    int count = 0;
    for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    }
    System.out.println(count);
  }
} public class Main{
  public static void main(String args[]){
    Scanner scanner = new Scanner(System.in);
    String S = scanner.next();
    String T = scanner.next();
    int count = 0;
    for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    }
    System.out.println(count);
  }
} Main
import java.util.Scanner;

public class Main{
  public static void main(String args[]){
    Scanner scanner = new Scanner(System.in);
    String S = scanner.next();
    String T = scanner.next();
    int count = 0;
    for(int i = 0;i < S.length();i++){
      if(S.charAt(i) == T.charAt(i)) continue;
      count++;
    }
    System.out.println(count);
  }
}