#include <iostream>
#include <fstream>

using namespace std;

ifstream f("nunta.in");
ofstream g("nunta.out");
const int NMAX=250;

int F1[NMAX],F2[NMAX],aux[NMAX],N;

void copiere(int A[],int B[])
{
    for (int i=0;i<=B[0];i++)
        A[i]=B[i];
}

void adunare(int A[],int B[])
{
    int T=0;
    for (int i=1;i<=A[0];i++)
    {
        T+=A[i]+B[i];
        A[i]=T%10;
        T/=10;
    }
    if (T>0) A[++A[0]]=1;
}

int main()
{
    f>>N;
    if (N<=3)
        g<<N;
    else
    {
        F1[0]=F2[0]=1;
        F1[1]=2;
        F2[1]=3;
        for (int i=4;i<=N;i++)
        {
            copiere(aux,F2);
            adunare(F2,F1);
            copiere(F1,aux);
        }
        for (int i=F2[0];i>=1;i--)
            g<<F2[i];
    }
    return 0;
}