import java.util.*;
 
class Main {
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    String S = sc.nextLine();
    String T = sc.nextLine();
    
    String[] Sar = S.split("");
    String[] Tar = T.split("");
    
    int c = 0;
    for(int i = 0; i < S.length(); i++){
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    }
    System.out.print(c);
  }
} import java.util.*; util.* java class Main {
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    String S = sc.nextLine();
    String T = sc.nextLine();
    
    String[] Sar = S.split("");
    String[] Tar = T.split("");
    
    int c = 0;
    for(int i = 0; i < S.length(); i++){
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    }
    System.out.print(c);
  }
} Main public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    String S = sc.nextLine();
    String T = sc.nextLine();
    
    String[] Sar = S.split("");
    String[] Tar = T.split("");
    
    int c = 0;
    for(int i = 0; i < S.length(); i++){
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    }
    System.out.print(c);
  } main {
    Scanner sc = new Scanner(System.in);
    String S = sc.nextLine();
    String T = sc.nextLine();
    
    String[] Sar = S.split("");
    String[] Tar = T.split("");
    
    int c = 0;
    for(int i = 0; i < S.length(); i++){
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    }
    System.out.print(c);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.nextLine(); S sc.nextLine() sc.nextLine sc String T = sc.nextLine(); T sc.nextLine() sc.nextLine sc String[] Sar = S.split(""); Sar S.split("") S.split S "" String[] Tar = T.split(""); Tar T.split("") T.split T "" int c = 0; c 0 for(int i = 0; i < S.length(); i++){
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    } {
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    } if(!Sar[i].equals(Tar[i])){
        c++;
      } !Sar[i].equals(Tar[i]) Sar[i].equals(Tar[i]) Sar[i].equals Sar[i] Sar i Tar[i] Tar i {
        c++;
      } c++ c System.out.print(c) System.out.print System.out System System.out c String args[] args
import java.util.*;
 
class Main {
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    String S = sc.nextLine();
    String T = sc.nextLine();
    
    String[] Sar = S.split("");
    String[] Tar = T.split("");
    
    int c = 0;
    for(int i = 0; i < S.length(); i++){
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    }
    System.out.print(c);
  }
}