Suresh is a fan of Mario. But being a programmer he decided to modify the game. In one module he needs your help. He modified the game as follows:
There are N stones on the way indexed from 1 to N. Every stone having index i is associated with points equal to i^th fibonacci number. That is if there are 5 stones then the points associated with them are 1,1,2,3,5 resp.
Mario gets the point when he steps on the stone. But during the gameplay he steps on M stones and skips some. So you have to find the sum of points Mario missed.

Input fomat:
First line contains 2 space separated integers containing N and M.
Next line contains M space separated integers denoting the points that he obtained.

Output format:
Print the sum of points Mario missed.

Constraints:
3 ≤ N ≤ 80
1 ≤ M ≤ N

SAMPLE INPUT
5 3
1 1 5

SAMPLE OUTPUT
5

Explanation

He missed the stones having points 2 and 3.
N, M = map(int, raw_input().split())
fib = [None] * N
fib[0], fib[1] = 1, 1
for i in range(2, N):
	fib[i] = fib[i - 1] + fib[i - 2]
a = [int(i) for i in raw_input().split()]
a.sort()
i, j, sumSkip = 0, 0, 0
while i < len(a) or j < len(fib):
	if i >= len(a) or a[i] != fib[j] :
		sumSkip += fib[j]
	else:
		i += 1
	j += 1
print sumSkip