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
 *
 * @author Hamadneh
 */
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);
        BMinorChange solver = new BMinorChange();
        solver.solve(1, in, out);
        out.close();
    }

    static class BMinorChange {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        }

    }
}
 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);
        BMinorChange solver = new BMinorChange();
        solver.solve(1, in, out);
        out.close();
    }

    static class BMinorChange {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        }

    }
} 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);
        BMinorChange solver = new BMinorChange();
        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);
        BMinorChange solver = new BMinorChange();
        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) BMinorChange solver = new BMinorChange(); solver new BMinorChange() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class BMinorChange {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        }

    } BMinorChange public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        } solve {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        } String s = in.next(); s in.next() in.next in String r = in.next(); r in.next() in.next in long c = 0; c 0 for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            } {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            } if (s.charAt(i) != r.charAt(i))
                    c++; s.charAt(i) != r.charAt(i) s.charAt(i) s.charAt s i r.charAt(i) r.charAt r i c++ c out.print(c) out.print out c 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);
        BMinorChange solver = new BMinorChange();
        solver.solve(1, in, out);
        out.close();
    }

    static class BMinorChange {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        }

    }
} 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);
        BMinorChange solver = new BMinorChange();
        solver.solve(1, in, out);
        out.close();
    }

    static class BMinorChange {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        }

    }
} 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
 *
 * @author Hamadneh
 */
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);
        BMinorChange solver = new BMinorChange();
        solver.solve(1, in, out);
        out.close();
    }

    static class BMinorChange {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String s = in.next();
            String r = in.next();
            long c = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) != r.charAt(i))
                    c++;
            }
            out.print(c);
        }

    }
}

