n,m = map(int,input().split())
a = list(map(lambda x:int(x)-1,input().split()))
b = [i for i in range(n)]
s = set()
for i in a:
    x,y = b[i],b[i+1]
    if x > y:
        x,y = y,x
    s.add(x * 10**7 + y)
    b[i],b[i+1] = b[i+1],b[i]
print(len(s))