#include <iostream>
#include <vector>
#include <sstream>

using namespace std;

class Fibs {
public:

	Fibs() {
		t.push_back(0);
		t.push_back(1);
	}

	int operator[]( int n ) {
		while ( n >= t.size() ) {
			t.push_back( t.rbegin()[0] + t.rbegin()[1] );
		}
		return t[n-1];
	}

protected:
	vector<int> t;
};

int main( int argc, char** argv ) {

	istringstream src;
	src.str( argv[1] );
	
	int n;
	src >> n;
		
	Fibs f;
	
	cout << f[n] << endl;

}