N, M = map(int, (input().split()))
AB = [list(map(int, input().split())) for _ in range(M)]
S = set()
for a, b in AB:
    S.add(a)
    S.add(b)
B = sorted(list(S))
D = dict(zip(B, range(len(B))))
NB = len(B)

dp = [0] * (NB)
AB.sort(key=lambda x: x[1])
k = 0
for i in range(1, NB):
    b = B[i]
    dp[i] = dp[i - 1]
    while k < M and AB[k][1] == b:
        dp[i] = max(dp[i], dp[D[AB[k][0]]] + 1)
        k += 1
print(2 * N - dp[NB - 1] - 2)