#include <iostream.h>
#include <fstream.h>
fstream f("nunta.in",ios::in);
fstream g("nunta.out",ios::out);
long long a,b,c,i,n;

int main ()
{
  f>>n;
  a=0;
  b=1;
  for (i=3;i<=n+1;i++)
	{
	  c=a+b;
	  a=b;
	  b=c;
	 }
  g<<c;
  f.close();
  g.close();
  return 0;
}