import java.util.*;

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

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