#include <bits/stdc++.h>
using namespace std;
const int sd = 21000;
const int NM = sd + sd + 2;
int a[NM];
int b[NM];
int c[NM];
int res[NM];
int dop[NM];
pair<int, int> p[NM];
pair<int, int> w[NM];
pair<int, int> w2[NM];
int main() {
  long long n;
  cin >> n;
  long long ans = n + n / 2;
  cout << ans;
  return 0;
}
