import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String S = in.nextLine();
    String T = in.nextLine();
    int N = S.length(), ans = 0;
    for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    }
    System.out.println(ans);
  }
} import java.util.Scanner; Scanner java.util public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String S = in.nextLine();
    String T = in.nextLine();
    int N = S.length(), ans = 0;
    for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    }
    System.out.println(ans);
  }
} Main public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String S = in.nextLine();
    String T = in.nextLine();
    int N = S.length(), ans = 0;
    for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    }
    System.out.println(ans);
  } main {
    Scanner in = new Scanner(System.in);
    String S = in.nextLine();
    String T = in.nextLine();
    int N = S.length(), ans = 0;
    for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    }
    System.out.println(ans);
  } Scanner in = new Scanner(System.in); in new Scanner(System.in) String S = in.nextLine(); S in.nextLine() in.nextLine in String T = in.nextLine(); T in.nextLine() in.nextLine in int N = S.length() N S.length() S.length S ans = 0; ans 0 for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    } int i = 0; int i = 0; i 0 i < N i N ++i ++i i {
    if(S.charAt(i) != T.charAt(i)) ++ans;
    } {
    if(S.charAt(i) != T.charAt(i)) ++ans;
    } if(S.charAt(i) != T.charAt(i)) ++ans; S.charAt(i) != T.charAt(i) S.charAt(i) S.charAt S i T.charAt(i) T.charAt T i ++ans ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String S = in.nextLine();
    String T = in.nextLine();
    int N = S.length(), ans = 0;
    for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    }
    System.out.println(ans);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String S = in.nextLine();
    String T = in.nextLine();
    int N = S.length(), ans = 0;
    for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    }
    System.out.println(ans);
  }
} Main
import java.util.Scanner;

public class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    String S = in.nextLine();
    String T = in.nextLine();
    int N = S.length(), ans = 0;
    for(int i = 0; i < N; ++i){
    if(S.charAt(i) != T.charAt(i)) ++ans;
    }
    System.out.println(ans);
  }
}