#include <iostream>

#include <vector>

using namespace std;

static auto fast_io = []

{

	ios::sync_with_stdio(false);

	cout.tie(nullptr);

	cin.tie(nullptr);

	return 0;

}();

int main()

{

	int n, a, x, y;

	while (cin >> n >> a, n + a)

	{

		// init

		vector<int> correct(n + 1, 0);

		vector<int> wrong(n + 1, 0);

		int max_num = (1 << n);

		int ret = 0;

		// input

		for (int i = 0; i < a; ++i)

		{

			cin >> x >> y;

			if (y > 0) correct[x] |= (1 << (y - 1));  // if 1 trust 3 and 4, correct[1] = 1100

			else wrong[x] |= (1 << (-y - 1));

		}

		for (int i = 0; i < max_num; ++i) // all possible combination

		{

			bool feasible = true;

			for (int j = 1; j <= n; ++j) // each person 

			{

				int p = 1 << (j - 1);

				if ((i & p) == 0) continue; // j doesn't exist in i

				if ((i & wrong[j]) != 0 || (i & correct[j]) != correct[j]) // is there a contradiction

				{

					feasible = false;

					break;

				}

			}

			if (feasible)

			{

				int cnt = 0, cpy = i;

				while (cpy) cnt += cpy & 1, cpy >>= 1; // count the number of '1' in i (bitwise)

				ret = max(ret, cnt);

			}

		}

		cout << ret << "\n";

	}

}