import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

	}
} Main public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

	} main {
		Scanner scan = new Scanner(System.in);

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

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

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

	}
} public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);

		String S = scan.next();
		String T = scan.next();
		int ans = 0;

		String[] splitedS = S.split("");
		String[] splitedT = T.split("");

		for(int i = 0;i < S.length(); i++) {
			if(!(splitedS[i].equals(splitedT[i]))) {
				ans++;
			}
		}

		System.out.println(ans);

	}
}