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

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见题面