#include <bits/stdc++.h>
using namespace std;
map<long long, long long> mp, mp1;
vector<pair<long long, pair<long long, long long> > > vpp, vpp1;
vector<pair<long long, long long> > vp, fin;
vector<long long> v, v1, v2, dummy;
map<pair<long long, long long>, long long> mpp;
map<long long, bool> mb;
long long n, k, a, b, c, d, ta, q, x, sum = 0, cnt = 0, s, m, y, l, req;
bool sortbysec(const pair<pair<long long, long long>, long long> &a,
               const pair<pair<long long, long long>, long long> &b) {
  return (a.second < b.second);
}
long long dp[200005 + 10];
void calc(long long n) {
  dp[0] = 1;
  for (long long i = 1; i <= n; i++) {
    dp[i] = ((dp[i - 1] % 998244353) * i) % 998244353;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  scanf("%lld", &n);
  long long ans = n / 3;
  ans *= 2;
  if (n % 3 != 0) ans++;
  printf("%lld\n", ans);
  return 0;
}
