#include <fstream>
using namespace std;
       ifstream in("nunta.in");
       ofstream out("nunta.out");
int fib1,fib2 ;
int fibo( int n )
{
     if( n % 2 )
     {
         fib1+=fib2;
     }
     else
     {
         fib1+=fib2;
         fib2+=fib2;
     }

}
int main()
{
    fib1=1;
    fib2=1;
     int n; in>>n;
     if( n==1 ) out<<1; else if ( n==2 )  out<<2;
     if ( n==3 )
     {
         for (int i=3; i<=n; i++)
            fibo(i);
     }
     out<<fib1+fib2;

    return 0;
}