#include"fstream"
using namespace std;
int n;



int main()
{
    ifstream fin("nunta.in");
    fin>>n;
    fin.close();
    
    int i,a,b,f=1;
    a=1;
    b=1;
    
    for(i=3;i<=n+1;++i)
         {
             f=a+b;
             a=b;
             b=f;
         }
    ofstream fout("nunta.out");
    fout<<f;
    fout.close();
    return 0;
}