import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 172_B
		Scanner sc = new Scanner(System.in);
		int iRes = 0;

		String str1 = sc.nextLine();
		String str2 = sc.nextLine();
		String[] strArray1 = str1.split("");
		String[] strArray2 = str2.split("");

		for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		}
		System.out.println(iRes);
	}

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

	public static void main(String[] args) {
		// TODO 172_B
		Scanner sc = new Scanner(System.in);
		int iRes = 0;

		String str1 = sc.nextLine();
		String str2 = sc.nextLine();
		String[] strArray1 = str1.split("");
		String[] strArray2 = str2.split("");

		for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		}
		System.out.println(iRes);
	}

} Main public static void main(String[] args) {
		// TODO 172_B
		Scanner sc = new Scanner(System.in);
		int iRes = 0;

		String str1 = sc.nextLine();
		String str2 = sc.nextLine();
		String[] strArray1 = str1.split("");
		String[] strArray2 = str2.split("");

		for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		}
		System.out.println(iRes);
	} main {
		// TODO 172_B
		Scanner sc = new Scanner(System.in);
		int iRes = 0;

		String str1 = sc.nextLine();
		String str2 = sc.nextLine();
		String[] strArray1 = str1.split("");
		String[] strArray2 = str2.split("");

		for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		}
		System.out.println(iRes);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int iRes = 0; iRes 0 String str1 = sc.nextLine(); str1 sc.nextLine() sc.nextLine sc String str2 = sc.nextLine(); str2 sc.nextLine() sc.nextLine sc String[] strArray1 = str1.split(""); strArray1 str1.split("") str1.split str1 "" String[] strArray2 = str2.split(""); strArray2 str2.split("") str2.split str2 "" for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		} int i = 0; int i = 0; i 0 i < str1.length() i str1.length() str1.length str1 i++ i++ i {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		} {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		} if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			} !strArray1[i].equals(strArray2[i]) strArray1[i].equals(strArray2[i]) strArray1[i].equals strArray1[i] strArray1 i strArray2[i] strArray2 i {
				iRes++;
			} iRes++ iRes System.out.println(iRes) System.out.println System.out System System.out iRes String[] args args public class Main {

	public static void main(String[] args) {
		// TODO 172_B
		Scanner sc = new Scanner(System.in);
		int iRes = 0;

		String str1 = sc.nextLine();
		String str2 = sc.nextLine();
		String[] strArray1 = str1.split("");
		String[] strArray2 = str2.split("");

		for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		}
		System.out.println(iRes);
	}

} public class Main {

	public static void main(String[] args) {
		// TODO 172_B
		Scanner sc = new Scanner(System.in);
		int iRes = 0;

		String str1 = sc.nextLine();
		String str2 = sc.nextLine();
		String[] strArray1 = str1.split("");
		String[] strArray2 = str2.split("");

		for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		}
		System.out.println(iRes);
	}

} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 172_B
		Scanner sc = new Scanner(System.in);
		int iRes = 0;

		String str1 = sc.nextLine();
		String str2 = sc.nextLine();
		String[] strArray1 = str1.split("");
		String[] strArray2 = str2.split("");

		for(int i = 0; i < str1.length(); i++) {
			if (!strArray1[i].equals(strArray2[i])) {
				iRes++;
			}
		}
		System.out.println(iRes);
	}

}
