import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.nextLine();
		char[] t = sc.next().toCharArray();
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		}
		System.out.println(ans);
	}
	
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.nextLine();
		char[] t = sc.next().toCharArray();
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		}
		System.out.println(ans);
	}
	
} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.nextLine();
		char[] t = sc.next().toCharArray();
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		}
		System.out.println(ans);
	} main {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.nextLine();
		char[] t = sc.next().toCharArray();
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		}
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) char[] s = sc.next().toCharArray(); s sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc sc.nextLine() sc.nextLine sc char[] t = sc.next().toCharArray(); t sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc int ans = 0; ans 0 for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		} 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]) {
				ans++;
			}
		} {
			if (s[i] !=  t[i]) {
				ans++;
			}
		} if (s[i] !=  t[i]) {
				ans++;
			} s[i] !=  t[i] s[i] s i t[i] t 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) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.nextLine();
		char[] t = sc.next().toCharArray();
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		}
		System.out.println(ans);
	}
	
} public class Main {
	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.nextLine();
		char[] t = sc.next().toCharArray();
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		}
		System.out.println(ans);
	}
	
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		char[] s = sc.next().toCharArray();
		sc.nextLine();
		char[] t = sc.next().toCharArray();
		int ans = 0;
		for (int i = 0; i < s.length; i++) {
			if (s[i] !=  t[i]) {
				ans++;
			}
		}
		System.out.println(ans);
	}
	
}
