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

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

const int length = 212;

void suma(short a[length], short b[length])
{
    int i, aux, t = 0;

    for(i = 1; i <= a[0] || i <= b[0] || t != 0; i++)
    {
        aux = a[i] + b[i] + t;

        a[i] = b[i];

        b[i] = aux % 10;

        t = aux / 10;
    }

    a[0] = b[0];

    b[0] = i - 1;
}

int main()
{
    int N, i;

    short a[length];
    short b[length];

    memset(a, 0, sizeof(a));
    memset(b, 0, sizeof(b));

    in >> N;

    a[0] = b[0] = 1;

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

    for(i = 3; i <= N; i++) suma(a, b);

    for(i = b[0]; i >= 1; i--) out << b[i];

    return 0;
}