POJ-3069-Saruman's Army

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const int maxn=1100;
int a[maxn],n,r;
int main()
{
while(scanf("%d%d",&r,&n)!=EOF)
{
if(r==-1&&n==-1)
break;
for(int i=0;i<n;i++)
scanf("%d",&a[i]);
sort(a,a+n);
int l,index=0,ans=0;
while(index<n)
{
l=a[index]+r;
while(index<n&&a[index]<=l)
index++;
int p=a[index-1]+r;
while(index<n&&a[index]<=p)
index++;
ans++;
}
printf("%d\n",ans);
}
return 0;
}