import java.io.PrintWriter;
import java.util.*;
import java.io.*;

public class Solver {

    public static void main(String[] args) {
        new Solver().stream();
    }

    final IO io = new IO();
    final PrintWriter out = new PrintWriter(System.out);

    void stream() {
        solve();
        out.flush();
    }

    void solve() {
        int N = io.Int();
        int M = (int)(1.5 * N);
        System.out.println(M);
    }
}

class IO {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1 << 12];
    private int ptr = 0, buffLen = 0;

    private boolean hasNextByte() {
        if (ptr < buffLen) return true;
        ptr = 0;
        try {
            buffLen = in.read(buffer);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return buffLen > 0;
    }

    private int readByte() {
        return hasNextByte() ? buffer[ptr++] : -1;
    }

    private boolean isPrintableChar(int c) {
        return 33 <= c && c <= 126;
    } //ASCII

    private void skipUnprintable() {
        while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;
    }

    private boolean hasNext() {
        skipUnprintable();
        return hasNextByte();
    }

    private String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while (isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    public String String() {
        return next();
    }

    public char Char() {
        return next().charAt(0);
    }

    public int Int() {
        return Integer.parseInt(next());
    }

    public long Long() {
        return Long.parseLong(next());
    }

    public double Double() {
        return Double.parseDouble(next());
    }

    public String[] StringArr(final int n) {
        final String[] arr = new String[n];
        for (int i = 0; i < n; ++i) arr[i] = String();
        return arr;
    }

    public char[] CharArr(final int n) {
        final char[] arr = new char[n];
        for (int i = 0; i < n; ++i) arr[i] = Char();
        return arr;
    }

    public int[] IntArr(final int n) {
        final int[] arr = new int[n];
        for (int i = 0; i < n; ++i) arr[i] = Int();
        return arr;
    }

    public long[] LongArr(final int n) {
        final long[] arr = new long[n];
        for (int i = 0; i < n; ++i) arr[i] = Long();
        return arr;
    }

    public double[] DoubleArr(final int n) {
        final double[] arr = new double[n];
        for (int i = 0; i < n; ++i) arr[i] = Double();
        return arr;
    }
}