参考答案：

#include<iostream>

using namespace std;

int main()
{
    long long  n;

    cin >> n;
    if (n % 3 == 0) cout << n / 3 * 2;
    else cout << n / 3 * 2 + 1;

    return 0;
}

Python:

num = int(input())
if num%3 == 0:
    print("%d" % ((num/3)*2))
else:
    print("%d" % ((num//3)*2+1))