#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int R, N;


int main()
{
	while (cin >> R >> N)
	{
		vector<int> data;
		if (R == -1 && N == -1)
			break;

		int x;
		for (int i = 0; i < N; i++)
		{
			cin >> x;
			data.push_back(x);
		}
		sort(data.begin(), data.end());

		int i = 0, ans = 0;
		while (i < N)
		{
			int s = data[i++];

			while (data[i] <= s + R && i < N)i++;

			int p = data[i - 1];

			while (data[i] <= p + R && i < N)i++;

			ans++;
		}

		cout << ans << "\n";

	}

	return 0;
}