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