Problem: 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

Solution (in PYTHON):

Solution:
l = [2, 1]
def a(N): 
    global l
    if(N == 0):
        return 2
    if(N == 1):
        return 1
    if(len(l) > N):
        return l[N]
    ans = a(N - 1) + a(N - 2)
    l.append(ans)
    return ans
    
N = input()
print a(N)