#include<stdio.h>
#include<queue>
#include<iostream>
#include<algorithm>
#include<math.h>
#include<string.h>
#define INF 0x3f3f3f3f
#define LL long long
#define MOD 100000007
#define MAXSIZE 10005

using namespace std;

int p[MAXSIZE];

int main()
{
    int r,n;
    while(scanf("%d%d",&r,&n),r!=-1 && n!=-1)
    {
        for(int i=0;i<n;i++)
            scanf("%d",&p[i]);
        sort(p,p+n);
        int ans = 0;
        int pos1=0,pos2=0;
        while(pos1 < n)
        {
            int index = p[pos1] + r;
            pos2 = pos1;
            while(p[pos2] <= index)
                pos2++;
            ans++;
            index = p[pos2-1] + r;
            pos1 = pos2;
            while(p[pos1] <= index)
                pos1++;
        }
        printf("%d\n",ans);
    }
    return 0;
}