#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;

ifstream in("nunta.in");
ofstream out("nunta.out");

# define length 205

char a[length];
char b[length];

short na, nb;

inline void suma()
{
    short i, aux, t = 0;

    for(i = 1; i <= na || i <= nb || t != 0; i++)
    {
        aux = (a[i] - '0') + (b[i] - '0') + t;

        a[i] = b[i];

        b[i] = (char)('0' + aux % 10);

        t = aux / 10;
    }

    na = nb;

    nb = i - 1;
}

int main()
{
    short i, N;

    in >> N;

    for(i = 0; i <= length; i++) a[i] = b[i] = '0';

    na = nb = 1;

    a[1] = '1';
    b[1] = '2';

    for(i = 3; i <= N; i++) suma();

    for(i = nb; i >= 1; i--) out << b[i];

    return 0;
}