#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using P = pair<int, int>;

const int INF = 1000000001;

int main(void)
{
  int n;
  cin >> n;

  int ans = n * 1.5;

  cout << ans << endl;
  return 0;
}