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<stdio.h>

int main(){
int a;
long int L[90];
scanf("%d", &a);
L[0] = 2;
L[1] = 1;
for(int i = 0; i <= a; i++) L[i + 2] = L[i + 1] + L[i];

printf("%ld\n", L[a]);
}