Springer

#include<stdio.h>
#include<cmath>
#include<algorithm>
using namespace std;

struct circle{
    double pos;
    double rad;
};

struct square{
    double L;
    double R;
/*  double lenght;
    double width;*/
};

double callenght(double r,double w){
    return sqrt((r*r)-(w*w));
}

bool Lcmp(square a,square b){
    return a.L < b.L;
}

double max(double a,double b){
    return (a > b ? a : b);
}

int main()
{
    int n;
    double l,w;
    scanf("%d %lf %lf",&n,&l,&w);

    circle Carr[n];
    for(int i = 0 ; i < n ; i ++){
        scanf("%lf %lf",&Carr[i].pos,&Carr[i].rad);
    }
    int sn = 0;
    square Sarr[n];
    for(int i = 0 ; i < n ; i ++){
        double pos = Carr[i].pos;
        double rad = Carr[i].rad;
        if(rad*2 + 1 < w)continue;
        double lenght = callenght(2*rad,w);
    //  printf("Test converse to square #%d (%.0lf,%.0lf) -> %lf -> [%lf,%lf]\n",i,pos,rad,lenght,pos - lenght/2 , pos + lenght/2);
        Sarr[sn++] = {pos - lenght/2 , pos + lenght/2};
    }
    sort(Sarr,Sarr+sn,Lcmp);
    double maxR = 0;
    double nxtR = -1;
    int ans = 0;
    for(int i = 0 ; i < sn ; ){
        double L = Sarr[i].L;
        double R = Sarr[i].R;
    //  printf("#%d : %lf %lf\n",i,L,R);
        if(R < 0)continue;
        if(L > l)break;
        if(L <= maxR){
            nxtR = max(nxtR , R);
            i ++;
        }
        else{
            if(nxtR == -1){
                printf("-1");
                return 0;
            }
            ans++;
            maxR = max(maxR,nxtR);
        //  if(maxR > l)break;
        //  printf("up to %lf\n",maxR);
            nxtR = -1;
        }
    }
    if(maxR < l && nxtR > maxR){
        maxR = nxtR;
        ans++;
    }
    if(maxR < l){
        printf("-1");
        return 0;
    }
    printf("%d",ans);
    return 0;
}
/*
3 8 0
2 3
4 2
7 2

3 5 0
1 1
2 1
4 1


*/