there is my code, its get WA on 9th test:

#include <iostream.h>
__int64 inline linea(long x1i,long y1i,long x2i,long y2i)
{return y2i-y1i;}
__int64 inline lineb(long x1i,long y1i,long x2i,long y2i)
{return x1i-x2i;}
__int64 inline linec(long x1i,long y1i,long x2i,long y2i)
{return y1i*x2i-x1i*y2i;}
int main()
{
    const long con=20000;
    long n,i,j,k,p1,p2;
    long x[con],y[con];
    __int64 a,b,c;
    cin>>n;
    p1=0;p2=1;
    for (i=1;i<n+1;i++){cin>>x[i]>>y[i];}
    for (i=1;i<n+1;i++)
    {
        if (p1==p2){break;}
        for (j=i+1;j<n+1;j++)
        {
        p1=0;p2=0;
        a=linea(x[i],y[i],x[j],y[j]);
        b=lineb(x[i],y[i],x[j],y[j]);
        c=linec(x[i],y[i],x[j],y[j]);
        for (k=1;k<i;k++)
        {
            if (-b*y[k]>=a*x[k]+c){p1++;}
            if (-b*y[k]<=a*x[k]+c){p2++;}
        }
        for (k=i+1;k<j;k++)
        {
            if (-b*y[k]>=a*x[k]+c){p1++;}
            if (-b*y[k]<=a*x[k]+c){p2++;}
        }
        for (k=j+1;k<n+1;k++)
        {
            if (-b*y[k]>=a*x[k]+c){p1++;}
            if (-b*y[k]<=a*x[k]+c){p2++;}
        }
        if (p1==p2) {cout<<i<<" "<<j;break;}
        }
    }
    return 0;
}
Can anybody help me?