#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
using T = tuple<int, int, int>;
#define al(a) a.begin(), a.end()
#define ral(a) a.rbegin(), a.rend()
#define sz(a) (int)a.size()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define db(a, b) cout << #a << ": " << a << " " << #b << ": " << b << endl;

int main() {
  int n;
  cin >> n;
  int ans = 0;
  rrep(i, n) {
    rrep(j, n) {
      if (i * 2 + j * 2 > n) break;
      ans = max(ans, i * 2 + j * 2);
    }
  }
  cout << ans << endl;
  return 0;
}