n,m = map(int,input().split())
l = []
for i in range(m):
    a,b = map(int,input().split())
    l.append((a,b))
l.sort(key = lambda x:(x[1],x[0]))
res = 0
right = 0
for a,b in l:
    if a >=right:
        res += 1
        right = b
print(2*(n-1)-res)