//见《挑战程序设计竞赛》第2.2.4节
#include<iostream>
#include<algorithm>
#define MAX_N 1000
using namespace std;
int N, R;
int X[MAX_N];
int main() {
while (cin >> R >> N, R != -1 && N != -1) {
for (int i = 0; i < N; i++) cin >> X[i];
sort(X, X + N);
int i = 0, ans = 0;
while (i < N) {
int s = X[i++];
while (i < N && X[i] <= s + R) i++;
int p = X[i - 1];
while (i < N && X[i] <= p + R) i++;
ans++;
}
cout << ans << endl;
}
return 0;
}
POJ_3069_Saruman's Army
