#include <iostream>
#include <fstream>

using namespace std;

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

void rez(unsigned long long k)
{
    int p;
    unsigned long long x,y,a;

    x=0;
    y=1;
    p=2;
    while(p<=k)
    {
        p++;
        a=x+y;
        x=y;
        y=a;
    }

    g<<a;
}

int main()
{
    unsigned long long k;

    f>>k;
    rez(k);

    return 0;
}