import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next(), T = sc.next();
    int num=0;
    for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    }
    System.out.println(num);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next(), T = sc.next();
    int num=0;
    for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    }
    System.out.println(num);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next(), T = sc.next();
    int num=0;
    for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    }
    System.out.println(num);
  } main {
    Scanner sc = new Scanner(System.in);
    String S = sc.next(), T = sc.next();
    int num=0;
    for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    }
    System.out.println(num);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.next() S sc.next() sc.next sc T = sc.next(); T sc.next() sc.next sc int num=0; num 0 for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    } int i=0; int i=0; i 0 i<S.length() i S.length() S.length S i++ i++ i {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    } {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    } if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      } !S.substring(i,i+1).equals(T.substring(i,i+1)) S.substring(i,i+1).equals(T.substring(i,i+1)) S.substring(i,i+1).equals S.substring(i,i+1) S.substring S i i+1 i 1 T.substring(i,i+1) T.substring T i i+1 i 1 {
        num++;
      } num++ num System.out.println(num) System.out.println System.out System System.out num String[] args args public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next(), T = sc.next();
    int num=0;
    for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    }
    System.out.println(num);
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next(), T = sc.next();
    int num=0;
    for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    }
    System.out.println(num);
  }
} Main
import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next(), T = sc.next();
    int num=0;
    for(int i=0; i<S.length(); i++) {
      if(!S.substring(i,i+1).equals(T.substring(i,i+1))) {
        num++;
      }
    }
    System.out.println(num);
  }
}