#include<fstream>
using namespace std;

ifstream cin("nunta.in");
ofstream cout("nunta.out");


short int  n,i,j,a[500],b[500],c[500];

void Adun(short int  a[],short int b[],short  int c[])
{
    c[0]=max(a[0],b[0]);
    int t=0,i;
    for (i=1;i<=c[0];i++)
    {
        c[i]=a[i]+b[i]+t;
        t=c[i]/10;
        c[i]%=10;
    }
    if (t)c[++c[0]]=t;
}

int main()
{
    cin>>n;

    if  (n<3){
        if (n==1)cout<<1;
         else cout<<2;
        return 0;
    }

    a[0]=a[1]=1;
    b[0]=1;b[1]=2;
    for (i=3;i<=n;i++)
    {
        Adun(a,b,c);
        for (j=0;j<=b[0];j++)a[j]=b[j];
        for (j=0;j<=c[0];j++)b[j]=c[j];
    }
    for (i=c[0];i;i--)cout<<c[i];
    return  0;
}