#include <cstdio>

using namespace std;

char v[2][212];
unsigned char lv[2];

int main()
{
    freopen("nunta.in", "r", stdin);
    freopen("nunta.out", "w", stdout);
    int n;
    scanf("%d", &n);
    lv[0] = 1;
    v[0][0] = 1;
    lv[1] = 1;
    v[1][0] = 2;
    if(n == 1) printf("1");
    else if(n == 2) printf("2");
    else
    {
        int i, r, a, b;
        for(int j = 2; j < n; j++)
        {
            a = j % 2;
            b = (j - 1) % 2;
            r = 0;
            for(i = 0; i < lv[a] || i < lv[b] || r != 0; i++)
            {
                r += v[a][i] + v[b][i];
                v[a][i] = r % 10;
                r /= 10;
            }
            lv[a] = i;
        }
        for(int i = lv[(i - 1) % 2] - 1; i >= 0; i--)
            printf("%d", v[(n - 1) % 2][i]);
    }
    return 0;
}