POJ 3069 Saruman's Army

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<stack>
#include<queue>
using namespace std;

int R , N;
int an[1010];

int cmp(const void *a ,const void *b)
{
    return *(int*)a-*(int*)b;
}

int main()
{
    while(scanf("%d%d",&R,&N)!=EOF)
    {
        if(R==-1 && N==-1)
            break;
        for(int i= 0;i<N;i++)
        {
            scanf("%d",&an[i]);
        }
        qsort(an,N,sizeof(int),cmp);
        int i=0;
        int ans=0;
        while(i<N)
        {
            int s = an[i++];
            while(i<N && an[i] <= s+R)
                i++;
            int p=an[i-1];
            while(i<N&& an[i]<=p+R)
                i++;
            ans++;
        }
        printf("%d\n",ans);
    }
	return 0;
}