n, m = list(map(int,input().split()))
t = list(map(int, input().split()))
li = [k for k in range(n)]
ptli = [None for i in range(m)]
for j in range(m):
  li[t[j]-1], li[t[j]] = li[t[j]], li[t[j]-1]
  ptli[j] = [li[t[j]-1], li[t[j]]]
whereli = [0 for i in range(n)]
for j in range(n):
  whereli[li[j]] = j
lili = [None for i in range(m)]
for j in range(m):
  li[whereli[ptli[j][0]]], li[whereli[ptli[j][1]]] = li[whereli[ptli[j][1]]], li[whereli[ptli[j][0]]]
  lili[j] = tuple(li)
  li[whereli[ptli[j][0]]], li[whereli[ptli[j][1]]] = li[whereli[ptli[j][1]]], li[whereli[ptli[j][0]]]
print(len(set(lili)))