Problem:
Score : 200 points

Problem Statement

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.

Sample Input 1

5

Sample Output 1

11

L_0=2

L_1=1

L_2=L_0+L_1=3

L_3=L_1+L_2=4

L_4=L_2+L_3=7

L_5=L_3+L_4=11

Thus, the 5-th Lucas number is 11.

Sample Input 2

86

Sample Output 2

939587134549734843

Solution in C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
int main() {
	int n;
	long int luca[86]={1,3,4,7,11,18,29,47,76,123,199,322,521,843,1364,2207,3571,5778,9349,15127,24476,39603,64079,103682,167761,271443,439204,710647,1149851,1860498,3010349,4870847,7881196,12752043,20633239,33385282,54018521,87403803,141422324,228826127,370248451,599074578,969323029,1568397607,2537720636,4106118243,6643838879,10749957122,17393796001,28143753123,45537549124,73681302247,119218851371,192900153618,312119004989,505019158607,817138163596,1322157322203,2139295485799,3461452808002,5600748293801,9062201101803,14662949395604,23725150497407,38388099893011,62113250390418,100501350283429,162614600673847,263115950957276,425730551631123,688846502588399,1114577054219522,1803423556807921,2918000611027443,4721424167835364,7639424778862807,12360848946698171,20000273725560978,32361122672259149,52361396397820127,84722519070079276,137083915467899403,221806434537978679,358890350005878082,580696784543856761,939587134549734843};
	scanf("%d", &n);
	printf("%ld", luca[n-1]);
	return 0;
}