
Score : 200 points
Problem StatementIt 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.
InputInput is given from Standard Input in the following format:
N
OutputPrint the N-th Lucas number.
Sample Input 15
Sample Output 111
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 286
Sample Output 2939587134549734843
