#include<iostream>
#include<algorithm>
#include<cmath>
using namespace std;
int f(int n){
	int sum;
	if (n == 1)return 1;
	if (n == 2)return 2;
	return sum=f(n-1)+f(n-2);
}
int main(){
	int n;
	cin>> n;
	cout << f(n);
	return 0;
}