import java.util.*;
import java.io.*;
class Main {

	//最大公約数・最小公倍数（セットで使う）
static int gcd (int a, int b) {return b>0?gcd(b,a%b):a;}
static int lcm (int a, int b) {return a*b/gcd(a,b);}

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

	//最大公約数・最小公倍数（セットで使う）
static int gcd (int a, int b) {return b>0?gcd(b,a%b):a;}
static int lcm (int a, int b) {return a*b/gcd(a,b);}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
      	
      	String s = sc.next();
      	String t = sc.next();
      	int cnt = 0;
      	
      	for(int i=0;i<s.length();i++){
        	if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          }
        }
      System.out.println(cnt);
      }
	} Main //最大公約数・最小公倍数（セットで使う）
static int gcd (int a, int b) {return b>0?gcd(b,a%b):a;} gcd {return b>0?gcd(b,a%b):a;} return b>0?gcd(b,a%b):a; b>0?gcd(b,a%b):a b>0 b 0 gcd(b,a%b) gcd b a%b a b a int a a int b b static int lcm (int a, int b) {return a*b/gcd(a,b);} lcm {return a*b/gcd(a,b);} return a*b/gcd(a,b); a*b/gcd(a,b) a*b a b gcd(a,b) gcd a b int a a int b b public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
      	
      	String s = sc.next();
      	String t = sc.next();
      	int cnt = 0;
      	
      	for(int i=0;i<s.length();i++){
        	if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          }
        }
      System.out.println(cnt);
      } main {
		Scanner sc = new Scanner(System.in);
      	
      	String s = sc.next();
      	String t = sc.next();
      	int cnt = 0;
      	
      	for(int i=0;i<s.length();i++){
        	if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          }
        }
      System.out.println(cnt);
      } 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 for(int i=0;i<s.length();i++){
        	if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          }
        } int i=0; int i=0; i 0 i<s.length() i s.length() s.length s i++ i++ i {
        	if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          }
        } {
        	if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          }
        } if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          } s.charAt(i) != t.charAt(i) s.charAt(i) s.charAt s i t.charAt(i) t.charAt t i {
            	cnt++;
          } cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args
import java.util.*;
import java.io.*;
class Main {

	//最大公約数・最小公倍数（セットで使う）
static int gcd (int a, int b) {return b>0?gcd(b,a%b):a;}
static int lcm (int a, int b) {return a*b/gcd(a,b);}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
      	
      	String s = sc.next();
      	String t = sc.next();
      	int cnt = 0;
      	
      	for(int i=0;i<s.length();i++){
        	if(s.charAt(i) != t.charAt(i)){
            	cnt++;
          }
        }
      System.out.println(cnt);
      }
	}