Problem: It is November 18 now in Japan. By the way, 11 and 18 are adjacent Lucas numbers.

You are given an integer N. Find the N-th Lucas number.

Here, the i-th Lucas number L_i is defined as follows:

* L_0=2
* L_1=1
* L_i=L_{i-1}+L_{i-2} (i≥2)

Constraints

* 1≤N≤86
* It is guaranteed that the answer is less than 10^{18}.
* N is an integer.

Input

Input is given from Standard Input in the following format:


N


Output

Print the N-th Lucas number.

Examples

Input

5


Output

11


Input

86


Output

939587134549734843

Solution (in CPP):

Solution:
#include<iostream>
using namespace std;
int main(){
	int n;
	cin >> n;
	long long ln_2,ln_1=-1,ln=2;
	for(int i=0;i<n;i++){
		ln_2=ln_1;
		ln_1=ln;
		ln=ln_2+ln_1;
	}
	cout<<ln<<endl;
}