#include <stdio.h>
#define N 1000
unsigned int X = 12345;
int rand_() {
return (X *= 3) >> 1;
}
long long cross2(int x1, int y1, int x2, int y2) {
return (long long) x1 * y2 - (long long) x2 * y1;
}
int xx[N], yy[N], n, o;
long long cross(int i, int j, int k) {
return cross2(xx[j] - xx[i], yy[j] - yy[i], xx[k] - xx[i], yy[k] - yy[i]);
}
void sort(int *ii, int l, int r) {
while (l < r) {
int i = l, j = l, k = r, i_ = ii[l + rand_() % (r - l)], tmp;
while (j < k) {
long long c = cross(o, ii[j], i_);
if (c == 0)
j++;
else if (c < 0) {
tmp = ii[i], ii[i] = ii[j], ii[j] = tmp;
i++, j++;
} else {
k--;
tmp = ii[j], ii[j] = ii[k], ii[k] = tmp;
}
}
sort(ii, l, i);
l = k;
}
}
int intersect(int i, int j, int k, int l) {
return (cross(i, j, k) > 0) != (cross(i, j, l) > 0) && (cross(k, l, i) > 0) != (cross(k, l, j) > 0);
}
int good(int i, int j) {
static int kk[N], ll[N];
int nk, nl, k, l, l_;
nk = 0, nl = 0;
for (k = 0; k < n; k++)
if (k != i && k != j) {
if (cross(i, j, k) > 0)
kk[nk++] = k;
else
ll[nl++] = k;
}
o = i, sort(kk, 0, nk), sort(ll, 0, nl);
for (k = 0, l = 0, l_ = -1; k < nk; k++) {
while (l < nl && cross(i, kk[k], ll[l]) < 0) {
if (l_ == -1 || cross(j, l_, ll[l]) < 0)
l_ = ll[l];
l++;
}
if (l_ != -1 && cross(j, l_, kk[k]) < 0)
return 0;
}
return 1;
}
int main() {
static int ii[N], uu[N * 3], vv[N * 3], ww[N * 3];
static char hull[N];
int m, h, i, cnt;
scanf("%d", &n);
o = -1;
for (i = 0; i < n; i++) {
scanf("%d%d", &xx[i], &yy[i]);
if (o == -1 || xx[o] > xx[i] || xx[o] == xx[i] && yy[o] > yy[i])
o = i;
ii[i] = i;
}
ii[0] = o, ii[o] = 0;
sort(ii, 1, n);
m = 0;
for (i = 0; i < n; i++) {
while (m >= 2 && cross(ii[m - 2], ii[m - 1], ii[i]) >= 0)
m--;
ii[m++] = ii[i];
}
cnt = m;
for (h = 0; h < m; h++)
hull[ii[h]] = 1;
for (h = 0; h + 2 < m; h++)
uu[h] = ii[0], vv[h] = ii[h + 1], ww[h] = ii[h + 2];
m -= 2;
for (i = 0; i < n; i++)
if (!hull[i]) {
for (h = 0; h < m; h++) {
int u = uu[h], v = vv[h], w = ww[h];
if (cross(i, u, v) < 0 && cross(i, v, w) < 0 && cross(i, w, u) < 0) {
while (h + 1 < m)
uu[h] = uu[h + 1], vv[h] = vv[h + 1], ww[h] = ww[h + 1], h++;
m--;
uu[m] = i, vv[m] = u, ww[m] = v, m++;
uu[m] = i, vv[m] = v, ww[m] = w, m++;
uu[m] = i, vv[m] = w, ww[m] = u, m++;
}
}
}
for (h = 0; h < m; h++) {
int u = uu[h], v = vv[h], w = ww[h];
if (good(u, v))
cnt++;
if (good(v, w))
cnt++;
if (good(w, u))
cnt++;
}
cnt /= 2;
printf("%d\n", cnt);
return 0;
}
