import sys
input = sys.stdin.readline
INF = 10 ** 18

n, m = map(int,input().split())
plan = sorted([list(map(int,input().split())) for _ in [0] * m], key = lambda x : x[1])

now = 0
ans = 2 * (n - 1)
for l, r in plan:
	if(now > l):
		continue
	now = r
	ans -= 1
print(ans)