N, M = map(int, input().split())
X = []
A = []
for _ in range(M):
    a, b = map(int, input().split())
    a -= 1
    b -= 1
    X.append((a, b))
    A.append(a)
    A.append(b)

SA = sorted(set(A))
IA = {a: i for i, a in enumerate(SA)}
X = [(IA[a], IA[b]) for a, b in X]
X.sort(key = lambda x: x[0])
Y = [0] * len(SA)
for a, b in X:
    Y[b] = max(Y[b], Y[a] + 1)
print((N - 1) * 2 - Y[-1])