import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
*/public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		Scanner in = new Scanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		B solver = new B();
		solver.solve(1, in, out);
		out.close();
	}
static class B   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    }

}
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util */public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		Scanner in = new Scanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		B solver = new B();
		solver.solve(1, in, out);
		out.close();
	}
static class B   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    }

}
} Main public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		Scanner in = new Scanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		B solver = new B();
		solver.solve(1, in, out);
		out.close();
	} main {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		Scanner in = new Scanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		B solver = new B();
		solver.solve(1, in, out);
		out.close();
	} InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) B solver = new B(); solver new B() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class B   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    }

} B public void solve(int testNumber, Scanner in, PrintWriter out) {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    } solve {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    } String S = in.next(); S in.next() in.next in String T = in.next(); T in.next() in.next in int ans = 0; ans 0 for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
            if (S.charAt(i) != T.charAt(i)) ans++;
        } {
            if (S.charAt(i) != T.charAt(i)) ans++;
        } if (S.charAt(i) != T.charAt(i)) ans++; S.charAt(i) != T.charAt(i) S.charAt(i) S.charAt S i T.charAt(i) T.charAt T i ans++ ans out.println(ans) out.println out ans int testNumber testNumber Scanner in in PrintWriter out out */public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		Scanner in = new Scanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		B solver = new B();
		solver.solve(1, in, out);
		out.close();
	}
static class B   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    }

}
} */public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		Scanner in = new Scanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		B solver = new B();
		solver.solve(1, in, out);
		out.close();
	}
static class B   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    }

}
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
*/public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		Scanner in = new Scanner(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		B solver = new B();
		solver.solve(1, in, out);
		out.close();
	}
static class B   {
public void solve(int testNumber, Scanner in, PrintWriter out) {
        // 入力
        String S = in.next();
        String T = in.next();
        int ans = 0;

        for (int i = 0; i < S.length(); i++) {
            if (S.charAt(i) != T.charAt(i)) ans++;
        }
        // 出力
        out.println(ans);

    }

}
}

