n,m=map(int,input().split())
p=[list(map(int,input().split())) for _ in range(m)]
p.sort(key=lambda x:x[1])
now=1;cost=0
for a,b in p:
    if now>a:
        continue
    cost+=(a-now)*2
    cost+=(b-a)*2-1
    now=b
print(cost+(n-now)*2)