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.
a = [0 for i in xrange(105)]
a[0] = 1
a[1] = 1
for i in xrange(2, 100):
	a[i] = a[i - 1] + a[i - 2]

n, m = map(int, raw_input().split())
ans = 0
x = map(int, raw_input().split())
a = a[:n]
for y in x:
	idx = -100
	for i in xrange(len(a)):
		if a[i] == y:
			idx = i
			break
	if idx != -100:
		del a[idx]

print sum(a)