#include <cstdio>

using namespace std;

char v[2][212];
unsigned char lv[3];

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

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
    {
        for(int i = 2; i < n; i++)
        {
            add(i % 2, (i - 1) % 2, i % 2);
        }
        for(int i = lv[(i - 1) % 2] - 1; i >= 0; i--)
            printf("%d", v[(n - 1) % 2][i]);
    }
    return 0;
}