import java.util.*;
import java.io.*;
class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    String T = sc.next();
    int cnt = 0;
    char Sc[] = S.toCharArray();
    char Tc[] = T.toCharArray();
    for(int i = 0, len = S.length(); i < len; i++){
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    }
    PrintWriter out = new PrintWriter(System.out);
    out.print(cnt);
    out.flush();
  }
} import java.util.*; util.* java import java.io.*; io.* java class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    String T = sc.next();
    int cnt = 0;
    char Sc[] = S.toCharArray();
    char Tc[] = T.toCharArray();
    for(int i = 0, len = S.length(); i < len; i++){
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    }
    PrintWriter out = new PrintWriter(System.out);
    out.print(cnt);
    out.flush();
  }
} Main public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    String T = sc.next();
    int cnt = 0;
    char Sc[] = S.toCharArray();
    char Tc[] = T.toCharArray();
    for(int i = 0, len = S.length(); i < len; i++){
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    }
    PrintWriter out = new PrintWriter(System.out);
    out.print(cnt);
    out.flush();
  } main {
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    String T = sc.next();
    int cnt = 0;
    char Sc[] = S.toCharArray();
    char Tc[] = T.toCharArray();
    for(int i = 0, len = S.length(); i < len; i++){
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    }
    PrintWriter out = new PrintWriter(System.out);
    out.print(cnt);
    out.flush();
  } 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 cnt = 0; cnt 0 char Sc[] = S.toCharArray(); Sc S.toCharArray() S.toCharArray S char Tc[] = T.toCharArray(); Tc T.toCharArray() T.toCharArray T for(int i = 0, len = S.length(); i < len; i++){
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    } int i = 0, len = S.length(); int i = 0 i 0 len = S.length(); len S.length() S.length S i < len i len i++ i++ i {
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    } {
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    } if(Sc[i] != Tc[i]){
        cnt++;
      } Sc[i] != Tc[i] Sc[i] Sc i Tc[i] Tc i {
        cnt++;
      } cnt++ cnt PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) out.print(cnt) out.print out cnt out.flush() out.flush out String args[] args
import java.util.*;
import java.io.*;
class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    String T = sc.next();
    int cnt = 0;
    char Sc[] = S.toCharArray();
    char Tc[] = T.toCharArray();
    for(int i = 0, len = S.length(); i < len; i++){
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    }
    PrintWriter out = new PrintWriter(System.out);
    out.print(cnt);
    out.flush();
  }
}