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.
def fib(n):
	l=[]
	n1=0
	n2=1
	n3=0
	l.append(n2)
	for i in range(n-1):
		n3=n1+n2
		l.append(n3)
		n1=n2
		n2=n3
	return l

def mario(n,m,l):
	p=[]
	p=fib(n)
	q=[]
	for i in p:
		if i not in l:
			q.append(i)
	if l.count(1)==1:
		q.append(1)

	print sum(q)

a=raw_input()
n,m=map(int,a.split())
b = raw_input()
l = map(int, b.split())


mario(n,m,l)