n, m = map(int, input().split())
segs = [None] * m
for i in range(m):
    segs[i] = tuple(map(int, input().split()))
segs = sorted(segs, key=lambda x: x[1])
ans = 0
r = -1
for seg in segs:
    if r <= seg[0]:
        ans += 1
        r = seg[1]
print(2 * n - 2 - ans)