mod = 998244353


def main():
    import sys
    input = sys.stdin.readline

    N, M = map(int, input().split())
    AB = []
    for _ in range(M):
        a, b = map(int, input().split())
        AB.append((a, b))
    AB.sort(key=lambda x: x[1])
    ans = 2 * (N - 1)
    r = 0
    for a, b in AB:
        if a < r:
            continue
        ans -= 1
        r = b
    print(ans)


if __name__ == '__main__':
    main()