#include <cstdio>

using namespace std;

struct BigNumber
{
    char v[220];
    unsigned char lv;

    void addTo(const BigNumber& a, BigNumber& rez)
    {
        int i, r = 0;
        for(i = 0; i < lv || i < a.lv || r != 0; i++)
        {
            r += v[i] + a.v[i];
            rez.v[i] = r % 10;
            r /= 10;
        }
        rez.lv = i;
    }

    void print()
    {
        for(int i = lv - 1; i >= 0; i--)
        {
            printf("%d", v[i]);
        }
    }
};

BigNumber v[3];

int main()
{
    freopen("nunta.in", "r", stdin);
    freopen("nunta.out", "w", stdout);
    int n;
    scanf("%d", &n);
    v[0].lv = 1;
    v[0].v[0] = 1;
    v[1].lv = 1;
    v[1].v[0] = 2;
    if(n == 1) v[0].print();
    else if(n == 2) v[1].print();
    else
    {
        for(int i = 2; i < n; i++)
        {
            v[(i - 2) % 3].addTo(v[(i - 1) % 3], v[i % 3]);
        }
        v[(n - 1) % 3].print();
    }
    return 0;
}