#include <iostream.h>
#include <fstream.h>
fstream f("nunta.in",ios::in);
fstream g("nunta.out",ios::out);
long long  a,b,c,n,i;
int main ()
{
  f>>n;
  a=0;b=1;
  for(i=2;i<=n+1;i++){  c=a+b;
			a=b;
			b=c;

		   }
 g<<c;
 f.close();
 g.close();
 return 0;
}