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.
t=raw_input()
t=t.split()
n=int(t[0])
m=int(t[1])
a=[0]*100

a[1]=1
a[2]=1
for i in range(3,90):
	a[i]=a[i-1]+a[i-2]


x=raw_input()
x=x.split()
count=0

for i in range(0,m):
	x[i]=int(x[i])
	if x[i]==1:
		count+=1
sum1=0




for i in range(3,n+1):
	if a[i] not in x:
		sum1+=a[i]

if count==1:
	sum1+=1
if count==0:
	sum1+=2
		
print sum1