N,M=map(int,input().split())
A=list(map(int,input().split()))
D=set()
P=[i for i in range(N)]
for i in range(M):
  pos=A[i]-1
  a,b=P[pos],P[pos+1]
  if a>b:
    a,b=b,a
  w=a*10**10+b
  D.add(w)
  P[pos],P[pos+1]=P[pos+1],P[pos]
print(len(D))