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();
    int count=0;
    for(int i=0;i<n;i++){
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    }
    System.out.print(count);
  }
} 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();
    int count=0;
    for(int i=0;i<n;i++){
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    }
    System.out.print(count);
  }
} 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();
    int count=0;
    for(int i=0;i<n;i++){
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    }
    System.out.print(count);
  } main {
    Scanner sc=new Scanner(System.in);
    String s=sc.next();
    String t=sc.next();
    int n=s.length();
    int count=0;
    for(int i=0;i<n;i++){
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    }
    System.out.print(count);
  } 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 int count=0; count 0 for(int i=0;i<n;i++){
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    } int i=0; int i=0; i 0 i<n i n i++ i++ i {
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    } {
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    } if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      } s.charAt(i)!=t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i {
        count=count+1;
      } count=count+1 count count+1 count 1 System.out.print(count) System.out.print System.out System System.out count 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();
    int count=0;
    for(int i=0;i<n;i++){
      if(s.charAt(i)!=t.charAt(i)){
        count=count+1;
      }
    }
    System.out.print(count);
  }
}