n, m = map(int, input().split())
shortcuts = [tuple(map(int, input().split())) for _ in range(m)]
shortcuts.sort(key=lambda x: (x[1], x[0]))

current_end = 0
count = 0

for a, b in shortcuts:
    if a >= current_end:
        count += 1
        current_end = b

print(2 * (n - 1) - count)