import java.util.*;

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