bzoj1914

#include<bits/stdc++.h>
using namespace std;
const int N = 100010;
const double pi = acos(-1);
struct points {
    double x, y, angle;
    points(double x = 0, double y = 0, double angle = 0) : x(x), y(y), angle(angle) {}
    bool friend operator < (points A, points B)
    {
        return A.angle < B.angle;
    }
} a[N];
int n, cnt, pos;
long long ans;
inline long long Sum(long long x)
{
    return x * (x - 1ll) * (x - 2ll) / 6ll;
}
inline long long calc(long long x)
{
    return x * (x - 1ll) / 2ll;
}
inline double A(double x)
{
    return x > 0 ? x : 2 * pi + x;
}
int main()
{
    scanf("%d", &n);
    ans = Sum(n);
    for(int i = 1; i <= n; ++i)
    {
        double x, y, angle;
        scanf("%lf%lf", &x, &y);
        angle = atan2(y, x);
        if(angle < 0) angle += 2 * pi;
        a[i] = points(x, y, angle);
    }
    sort(a + 1, a + n + 1);
    for(int i = 2; i <= n; ++i) if(a[i].angle - a[1].angle > pi) 
    {
        pos = i;
        break;
    }
    cnt = pos - 1;
    for(int i = 1; i <= n; ++i)
    {
        --cnt;
        while(A(a[pos].angle - a[i].angle) < pi && pos != i) 
        {
            ++pos;
            pos = (pos - 1) % n + 1;
            ++cnt;
        }
        ans -= calc(cnt);
    }
    printf("%lld\n", ans);
    return 0;
}