#include <iostream>
#include <fstream>

using namespace std;

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

typedef long long lint;
typedef unsigned long long ulint;

int n, i;
ulint a, b, c;

int main()
{
    f >> n;

    if(n == 1) {
        g << 1; return 0;
    }

    a = 1; b = 1;
    for(i = 2; i <= n; i ++)  {
        c = a + b;
        a = b;
        b = c;
    }

    g << c << '\n';

    f.close();
    g.close();
    return 0;
}