#include <iostream>
#include <fstream>

using namespace std;

ifstream f("nunta.in");
ofstream g("nunta.out");

int main()
{
    int a[999], b[999], c[999], i, j, N, rest=0;
    f>>N;

    a[0]=1; a[1]=1;
    b[0]=1; b[1]=2;

    for (i=3; i<=N; i++) {
    rest=0;
    if (b[0]>a[0])
    { for (j=a[0]+1; j<=b[0]; ) a[j++]=0;
      a[0]=b[0]; }

    for (j=1;j<=a[0];j++)
    { a[j]+=b[j]+rest;
      rest=a[j]/10;
      a[j]%=10; }

  if (rest) a[++a[0]]=rest;

    for (j=0; j<=b[0]; j++) c[j]=b[j];
    for (j=0; j<=a[0]; j++) b[j]=a[j];
    for (j=0; j<=c[0]; j++) a[j]=c[j];

    }
    for (i=b[0]; i>0; i--) g<<b[i];
    f.close();
    g.close();
    return 0;
}