import sys
input = sys.stdin.readline

N,M=map(int,input().split())
AB=[list(map(int,input().split())) for _ in range(M)]
AB.sort(key=lambda x:x[1])
end=0
ans=(N-1)*2
for a,b in AB:
    if end<=a:
        end=b
        ans-=1
print(ans)