import java.util.*;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		char[] S = scan.next().toCharArray();
		char[] T = scan.next().toCharArray();
		int count = 0;
		for(int i = 0; i < S.length; i++) {
			if(S[i] != T[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} import java.util.*; util.* java public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		char[] S = scan.next().toCharArray();
		char[] T = scan.next().toCharArray();
		int count = 0;
		for(int i = 0; i < S.length; i++) {
			if(S[i] != T[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		char[] S = scan.next().toCharArray();
		char[] T = scan.next().toCharArray();
		int count = 0;
		for(int i = 0; i < S.length; i++) {
			if(S[i] != T[i]) {
				count++;
			}
		}
		System.out.println(count);
	} main {
		Scanner scan = new Scanner(System.in);
		char[] S = scan.next().toCharArray();
		char[] T = scan.next().toCharArray();
		int count = 0;
		for(int i = 0; i < S.length; i++) {
			if(S[i] != T[i]) {
				count++;
			}
		}
		System.out.println(count);
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) char[] S = scan.next().toCharArray(); S scan.next().toCharArray() scan.next().toCharArray scan.next() scan.next scan char[] T = scan.next().toCharArray(); T scan.next().toCharArray() scan.next().toCharArray scan.next() scan.next scan int count = 0; count 0 for(int i = 0; i < S.length; i++) {
			if(S[i] != 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] != T[i]) {
				count++;
			}
		} {
			if(S[i] != T[i]) {
				count++;
			}
		} if(S[i] != T[i]) {
				count++;
			} S[i] != T[i] S[i] S i T[i] T i {
				count++;
			} count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		char[] S = scan.next().toCharArray();
		char[] T = scan.next().toCharArray();
		int count = 0;
		for(int i = 0; i < S.length; i++) {
			if(S[i] != T[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		char[] S = scan.next().toCharArray();
		char[] T = scan.next().toCharArray();
		int count = 0;
		for(int i = 0; i < S.length; i++) {
			if(S[i] != T[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

} Main
import java.util.*;

public class Main {

	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		char[] S = scan.next().toCharArray();
		char[] T = scan.next().toCharArray();
		int count = 0;
		for(int i = 0; i < S.length; i++) {
			if(S[i] != T[i]) {
				count++;
			}
		}
		System.out.println(count);
	}

}