N,M=map(int,input().split())
X=[tuple(map(int,input().split())) for i in range(M)]
X.sort(key=lambda x:x[1])
ANS=2*N-2
v=0
for i in range(M):
  if v<=X[i][0]:
    v=X[i][1]
    ANS-=1
print(ANS)