#include<fstream>

using namespace std;

#define INPUTFILE "fractii.in"
#define OUTPUTFILE "fractii.out"

ifstream fin (INPUTFILE);
ofstream fout (OUTPUTFILE);

int main()
{
    int n,i,aux,a,b;
    fin>>n;
    if(n==1)
            fout<<"1";
    else
    {
        a=3;
        b=7;
        for(i=2; i<=n-1; ++i)
        {
                 aux=a+b+1;
                 a=b;
                 b=aux;
        }
        fout<<a;
    }
    return 0;
}