n,m = map(int,input().split())
ms = [list(map(int,input().split())) for i in range(m)]


ms.sort(reverse = True)
now = n
ans = 0
for s,t in ms:
    if now >= t:
        ans += (now - t)*2
        now = s
        ans += t*2 - s*2 - 1

ans+=(now-1)*2

print(ans)