额，，一看就设抛物线是y=a*x^2+b*x，把x，y1,y2带进去就是关于a，b的不等式。。然后半平面交。。。

考虑答案，可以二分。

（然而还是不对，，被卡精度了23333，（话说百度卡常数，，直接连膝盖都没了。。），，而且开始的时候异常自信，直接没加边界，就搞搞搞23333，闷声做大死2333）

1 #include
     
       2 #define N 100005 3 #define LL long long  4 #define eps 1e-8 5 #define double long double 6 using namespace std; 7 inline int ra() 8 { 9     int x=0,f=1; char ch=getchar();10     while (ch<'0' || ch>'9') {
   if (ch=='-') f=-1; ch=getchar();}11     while (ch>='0' && ch<='9') {x=x*10+ch-'0'; ch=getchar();}12     return x*f;13 }14 int n,cnt,tot;15 const double linf=1e15;16 struct in_data{
   double x,y1,y2;} q[N];17 struct point{
   double x,y;};18 struct line{19     point a,b; double angle;20     void print()21     {22         printf("%.1lf   %.1lf   %.1lf   %.1lf\n",a.x,a.y,b.x,b.y);23     }24 } l[N<<1],s[N<<1];25 double operator * (point a, point b){26     return a.x*b.y-a.y*b.x;27 }28 point operator - (point a, point b){29     point t; t.x=a.x-b.x; t.y=a.y-b.y; return t;30 }31 bool operator < (line a, line b){32     if (a.angle==b.angle) return (b.b-a.a)*(a.b-a.a)>0;33     return a.angle
      
       =2;65 }66 bool check(int len)67 {68     cnt=0;69     if (len<=2) return 1;70     for (int i=1; i<=len; i++)71     {72         l[++cnt].a.x=-1; l[cnt].a.y=q[i].y1/q[i].x+q[i].x;73         l[cnt].b.x=1; l[cnt].b.y=q[i].y1/q[i].x-q[i].x;74         l[++cnt].a.x=1; l[cnt].a.y=q[i].y2/q[i].x-q[i].x;75         l[cnt].b.x=-1; l[cnt].b.y=q[i].y2/q[i].x+q[i].x;76     }77     l[++cnt].a=(point){-linf,-linf};l[cnt].b=(point){linf,-linf};78     l[++cnt].a=(point){linf,-linf};l[cnt].b=(point){linf,linf};79     l[++cnt].a=(point){linf,linf};l[cnt].b=(point){-linf,linf};80     l[++cnt].a=(point){-linf,linf};l[cnt].b=(point){-linf,-linf};81     for (int i=1; i<=cnt; i++)82         l[i].angle=atan2(l[i].b.y-l[i].a.y,l[i].b.x-l[i].a.x);83     sort(l+1,l+cnt+1);84     return half_plane_intersection();85 }86 int main()87 {88     n=ra();89     for (int i=1; i<=n; i++) q[i].x=ra(),q[i].y1=ra(),q[i].y2=ra();90     int L=1,R=n,ans;91     while (L<=R)92     {93         int mid=L+R>>1;94         if (check(mid)) ans=mid,L=mid+1; 95             else R=mid-1; 96     }97     cout<