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]
Z = [[] for _ in range(len(SA))]
for a, b in X:
    Z[a].append(b)
Y = [0] * len(SA)

for i in range(len(SA)):
    Y[i] = max(Y[i], Y[i-1])
    for j in Z[i]:
        Y[j] = max(Y[j], Y[i] + 1)
print((N - 1) * 2 - Y[-1])