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; } }