UVa 10382 Watering Grass

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
const int MAXN = 10001;
struct node
{
    double s,t;
    bool operator < (const node& x) const
    {
        if(s!=x.s)
            return s <x.s;
        else
            return t >x.t;
    }
};
int main()
{
    int n,cnt;
    double w,l,p,r;
    struct node num[MAXN];
    int st;
    while(scanf("%d%lf%lf",&n,&l,&w)!=EOF)
    {
        st=0;
        for(int i=0;i<n;i++)
        {
            scanf("%lf%lf",&p,&r);
            if(r>=w/2.0)
            {
                num[st].s=p-sqrt(r*r-w*w/4.0);
                num[st].t=p+sqrt(r*r-w*w/4.0);
                if(num[st].s<0)
                    num[st].s=0;
                if(num[st].t>l)
                    num[st].t=l;
                st++;
            }
        }
        sort(num,num+st);
      //  for(int i=0;i<st;i++)
      //      printf("%lf %lf\n",num[i].s,num[i].t);
        double a=num[0].s,b=num[0].t;
        cnt=1;
        for(int i=1;i<st;i++)
            if(num[i].s>b)
                break;
            else if(num[i].s<=a && num[i].t>b)
                b=num[i].t;
            else if(num[i].s>a && num[i].t>b)
                a=b,b=num[i].t,cnt++;
        if(num[0].s>0 || b<l)
            printf("-1\n");
        else
            printf("%d\n",cnt);
    }
    return 0;
}