n, m = map(int, input().split())
lis = [list(map(int, input().split())) for _ in range(m)]
lis.sort(key=lambda x:x[1])
B = [1] * n
for i in range(m):
	for j in range(lis[i][0]-1, lis[i][-1]):
		if B[j] == 0:
			break
	else:
		B[lis[i][-1]-1] = 0
print(sum(B))