N, M = map(int, input().split())
D = []
for i in range(M):
    A, B = map(int, input().split())
    D.append((A, B))
    
D.sort(reverse=True)
ans = 2 * N - 2
pre = 10 ** 18
for a, b in D:
    if b <= pre:
        ans -= 1
        pre = a
print(ans)