d702

//d702

#include <iostream>
#include <stdlib.h>
using namespace std;
int main()
{
    int  n;
    while (cin >> n)
    {
        unsigned long  count[1000][3]; // 0 = x,1 = 1,or 2's 2 , 2 = 1
        count[n - 1][0] = 0;
        count[n - 1][1] = 1;
        count[n - 1][2] = 0;
        if (n > 1)
        {
            count[n - 2][0] = 1;
            count[n - 2][1] = 0;
            count[n - 2][2] = 1;
        }
        for (unsigned long i = n - 2; i > 0; i--)
        {
            count[i - 1][0] = count[i][1] + count[i][2];
            count[i - 1][1] = count[i][0];
            count[i - 1][2] = count[i][1];
        }

        cout << count[0][1] + count[0][2] << endl;

    }
}