n,m = map(int,input().split())
ms = [list(map(int,input().split())) for i in range(m)]
ms.sort(key=lambda x:(x[1],x[0]),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)

# 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)