#include <fstream>
#include <iostream>
using namespace std;


int main () {

long long n,a,b,c;

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

f>>n;

or (i=3;i<=n+1;i++) {
                        c=a+b;
                        a=b;
			b=c;
			}
     

cout<<b;

f.close();
g.close();

return 0;

}