#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, n, c, d, i, j, k, l, ans;
  while (cin >> n) {
    ans = (2 * n) / 3;
    if ((2 * n) % 3 == 1) cout << ans << endl;
    if ((2 * n) % 3 == 2) cout << ans + 1 << endl;
    if ((2 * n) % 3 == 0) cout << ans << endl;
  }
  return 0;
}
