#include <cstdio>

using namespace std;

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

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

void print(const BigNumber& a)
{
    for(int i = a.lv - 1; i >= 0; i--)
    {
        printf("%d", a.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) print(v[0]);
    else if(n == 2) print(v[1]);
    else
    {
        for(int i = 2; i < n; i++)
        {
            add(v[(i - 2) % 3], v[(i - 1) % 3], v[i % 3]);
        }
        print(v[(n - 1) % 3]);
    }
    return 0;
}