import java.util.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
      	String str1 = sc.next();
        char[] ch1 = getChars(str1);
      	String str2 = sc.next();
      	char[] ch2 = getChars(str2);

      	int count = 0;
      	for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        }

      	System.out.println(count);
    }
  
  	public static char[] getChars(String str) {
      	char[] ch = new char[str.length()];
      	for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        }
      	return ch;
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
      	String str1 = sc.next();
        char[] ch1 = getChars(str1);
      	String str2 = sc.next();
      	char[] ch2 = getChars(str2);

      	int count = 0;
      	for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        }

      	System.out.println(count);
    }
  
  	public static char[] getChars(String str) {
      	char[] ch = new char[str.length()];
      	for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        }
      	return ch;
    }
} Main public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
      	String str1 = sc.next();
        char[] ch1 = getChars(str1);
      	String str2 = sc.next();
      	char[] ch2 = getChars(str2);

      	int count = 0;
      	for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        }

      	System.out.println(count);
    } main {
		Scanner sc = new Scanner(System.in);
      	String str1 = sc.next();
        char[] ch1 = getChars(str1);
      	String str2 = sc.next();
      	char[] ch2 = getChars(str2);

      	int count = 0;
      	for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        }

      	System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String str1 = sc.next(); str1 sc.next() sc.next sc char[] ch1 = getChars(str1); ch1 getChars(str1) getChars str1 String str2 = sc.next(); str2 sc.next() sc.next sc char[] ch2 = getChars(str2); ch2 getChars(str2) getChars str2 int count = 0; count 0 for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        } int i=0; int i=0; i 0 i<str1.length() i str1.length() str1.length str1 i++ i++ i {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        } {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        } if(ch1[i] != ch2[i]) {
            count++;
          } ch1[i] != ch2[i] ch1[i] ch1 i ch2[i] ch2 i {
            count++;
          } count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public static char[] getChars(String str) {
      	char[] ch = new char[str.length()];
      	for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        }
      	return ch;
    } getChars {
      	char[] ch = new char[str.length()];
      	for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        }
      	return ch;
    } char[] ch = new char[str.length()]; ch new char[str.length()] str.length() str.length str for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        } int i=0; int i=0; i 0 i<str.length() i str.length() str.length str i++ i++ i {
            ch[i] = str.charAt(i);
        } {
            ch[i] = str.charAt(i);
        } ch[i] = str.charAt(i) ch[i] ch i str.charAt(i) str.charAt str i return ch; ch String str str public class Main {
    public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
      	String str1 = sc.next();
        char[] ch1 = getChars(str1);
      	String str2 = sc.next();
      	char[] ch2 = getChars(str2);

      	int count = 0;
      	for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        }

      	System.out.println(count);
    }
  
  	public static char[] getChars(String str) {
      	char[] ch = new char[str.length()];
      	for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        }
      	return ch;
    }
} public class Main {
    public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
      	String str1 = sc.next();
        char[] ch1 = getChars(str1);
      	String str2 = sc.next();
      	char[] ch2 = getChars(str2);

      	int count = 0;
      	for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        }

      	System.out.println(count);
    }
  
  	public static char[] getChars(String str) {
      	char[] ch = new char[str.length()];
      	for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        }
      	return ch;
    }
} Main
import java.util.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
      	String str1 = sc.next();
        char[] ch1 = getChars(str1);
      	String str2 = sc.next();
      	char[] ch2 = getChars(str2);

      	int count = 0;
      	for (int i=0; i<str1.length(); i++) {
          if(ch1[i] != ch2[i]) {
            count++;
          }
        }

      	System.out.println(count);
    }
  
  	public static char[] getChars(String str) {
      	char[] ch = new char[str.length()];
      	for (int i=0; i<str.length(); i++) {
            ch[i] = str.charAt(i);
        }
      	return ch;
    }
}