#include <bits/stdc++.h>
using namespace std;

int main() {
long long n;  // 用long long防止溢出
    cin >> n;
    long long ans = n / 3 * 2;  
    int rem = n % 3;
    if (rem == 2)
        ans += 1;
    
    cout << ans << endl;
    return 0;
}

#include <bits/stdc++.h>

using namespace std;

int main() {

long long n; // 用long long防止溢出 cin >> n;

long long ans = n / 3 * 2; 

int rem = n % 3;

if (rem == 2)

    ans += 1;
    
cout << ans << endl;

return 0;

}