import java.util.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    String t = sc.next();
    int n =s.length(), res = 0;
    
    for(int i = 0; i < n; i++) {
      if(s.charAt(i) != t.charAt(i))
        res++;
    }
    
    System.out.println(res);
  }
} import java.util.*; util.* java class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    String t = sc.next();
    int n =s.length(), res = 0;
    
    for(int i = 0; i < n; i++) {
      if(s.charAt(i) != t.charAt(i))
        res++;
    }
    
    System.out.println(res);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    String t = sc.next();
    int n =s.length(), res = 0;
    
    for(int i = 0; i < n; i++) {
      if(s.charAt(i) != t.charAt(i))
        res++;
    }
    
    System.out.println(res);
  } main {
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    String t = sc.next();
    int n =s.length(), res = 0;
    
    for(int i = 0; i < n; i++) {
      if(s.charAt(i) != t.charAt(i))
        res++;
    }
    
    System.out.println(res);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String s = sc.next(); s sc.next() sc.next sc String t = sc.next(); t sc.next() sc.next sc int n =s.length() n s.length() s.length s res = 0; res 0 for(int i = 0; i < n; i++) {
      if(s.charAt(i) != t.charAt(i))
        res++;
    } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
      if(s.charAt(i) != t.charAt(i))
        res++;
    } {
      if(s.charAt(i) != t.charAt(i))
        res++;
    } if(s.charAt(i) != t.charAt(i))
        res++; s.charAt(i) != t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i res++ res System.out.println(res) System.out.println System.out System System.out res String[] args args
import java.util.*;

class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    String t = sc.next();
    int n =s.length(), res = 0;
    
    for(int i = 0; i < n; i++) {
      if(s.charAt(i) != t.charAt(i))
        res++;
    }
    
    System.out.println(res);
  }
}
