#include <fstream>

using namespace std;
ifstream fin ("kfib.in");
ofstream fout ("kfib.out");
int main()
{
    long long a,b,i=0,n,aux;
    fin>>n;
    i=2;
    a=0;
    b=1;
    while (i<=n)
    {
        aux=a+b;
        a=b;
        b=aux;
        i++;
    }
    fout<<aux;
    fin.close();
    fout.close();
    return 0;
}