import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		sc.close();
		int i=0;
		int ans = 0;
		while(!Arrays.equals(S, T)){
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		}
		System.out.println(ans);
	}
} import java.util.*; util.* java class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		sc.close();
		int i=0;
		int ans = 0;
		while(!Arrays.equals(S, T)){
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		}
		System.out.println(ans);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		sc.close();
		int i=0;
		int ans = 0;
		while(!Arrays.equals(S, T)){
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		}
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		sc.close();
		int i=0;
		int ans = 0;
		while(!Arrays.equals(S, T)){
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		}
		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 char[] T = sc.next().toCharArray(); T sc.next().toCharArray() sc.next().toCharArray sc.next() sc.next sc sc.close() sc.close sc int i=0; i 0 int ans = 0; ans 0 while(!Arrays.equals(S, T)){
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		} !Arrays.equals(S, T) Arrays.equals(S, T) Arrays.equals Arrays S T {
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		} if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			} T[i]!=S[i] T[i] T i S[i] S i {
				S[i]=T[i];
				ans++;
			} S[i]=T[i] S[i] S i T[i] T i ans++ ans i++ i System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		sc.close();
		int i=0;
		int ans = 0;
		while(!Arrays.equals(S, T)){
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		}
		System.out.println(ans);
	}
}
