#include<bits/stdc++.h>

#define fi first
#define se second

using namespace std;

typedef pair<double, int> PDI;

const int N = 2e3 + 10;

struct point
{
    int x, y;
};
point q[N];
int stk[N], top;
bool used[N];
PDI g[N];

point operator- (point a, point b)
{
    return {a.x - b.x, a.y - b.y};
}

int cross(point a, point b)
{
    return a.x * b.y - a.y * b.x;
}

int area(point a, point b, point c)
{
    return cross(b - a, c - a);
}

void perfect()
{
    int n;
    cin >> n;
    for(int i = 1; i <= n; i ++)
        cin >> q[i].x >> q[i].y;
    sort(q + 1, q + 1 + n, [&](point a, point b)
    {
        if(a.x !=b.x) return a.x < b.x;
        return a.y < b.y;
    });
    for(int i = 1; i <= n; i ++)
    {
        while(top >= 2 && area(q[stk[top - 1]], q[stk[top]], q[i]) > 0)
            used[stk[top --]] = false;
            
        stk[++ top] = i;
        used[i] = true;
    }
    
    used[1] = false;
    for(int i = n; i >= 1; i --)
    {
        if(used[i]) continue;
        while(top >= 2 && area(q[stk[top - 1]], q[stk[top]], q[i]) > 0)
            used[stk[top --]] = false;
            
        stk[++ top] = i;
        used[i] = true;
    }
    int ans = 0;
    for(int i = 1; i <= n; i ++)
    {
        if(used[i]) continue;
        int id = 0;
        for(int j = 1; j <= n; j ++)
        {
            if(j == i) continue;
            g[++ id] = {atan2(q[j].y - q[i].y, q[j].x - q[i].x), j};
        }
        sort(g + 1, g + 1 + id, [&](PDI a, PDI b)
        {
            return a.fi < b.fi;
        });
        for(int j = 1; j <= id; j ++)
            if(used[g[j].se] && used[g[j % id + 1].se]) ans ++;
    }
    cout << ans + 1 << endl;
}

int main()
{
    int T = 1;
    while(T --) perfect();
    return 0;
}