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)

Input

Input is given from Standard Input in the following format:
N

Output

Print the N-th Lucas number.

Constraints

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

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

见题面 Input 部分

见题面 Output 部分