#include <iostream>
#include <fstream>


using namespace std;
ifstream fi("nunta.in");
ofstream fo("nunta.out");
int nr1[1000],nr2[1000];
void adun(int vect1[],int vect2[])
{
    for(int i=1;i<=max(vect1[0],vect2[0]);i++)
    {
        vect1[i]=vect1[i]+vect2[i];
        if(i==max(vect1[0],vect2[0]) && vect1[i]/10!=0)
        {
            vect1[i+1]+=vect1[i]/10;
            vect1[i]%=10;
            vect1[0]++;
        }
        else if(vect1[i]/10!=0)
        {
            vect1[i+1]+=vect1[i]/10;
            vect1[i]%=10;
        }
    }
}

int main()
{
    int n,i;
    fi>>n;
    nr1[0]=1;
    nr2[0]=1;
    nr2[1]=2;
    nr1[1]=1;
    if(n==1)
        fo<<nr1[1];
    else if(n==2)
        fo<<nr2[1];
    else
    {
    for( i=3;i<=n;i++)
    {
        if(i%2!=0)
            adun(nr1,nr2);
        else
            adun(nr2,nr1);
    }
    if((i-1)%2==0)
    {
        for(int j=nr2[0];j>=1;j--)
            fo<<nr2[j];
    }
    else
    {
        for(int j=nr1[0];j>=1;j--)
            fo<<nr1[j];
    }
    }


}