n,m=map(int,input().split())
from operator import itemgetter
p=[list(map(int,input().split())) for i in [0]*m]
p.sort(key=itemgetter(1))

now=0
ans=2*(n-1)
for l,r in p:
    if (now>l):
        continue
    now=r
    ans-=1

print(ans)