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