#include <stdio.h>
#include <stdlib.h>
#include <math.h>
double polar(double,double);
void qs(int,int);
void sw(double *a,double *b);
void init();
int caut_bin(int,int,int,int);
int n;
double x[1501],y[1501],h[1501];
double polar(double x,double y)
{
if (x>0)
{
if (y>0) return atan(y/x); else
return atan(y/x)+3.14*3;
} else
if (x<0) return 3.14+atan(y/x); else
if (x==0)
{
if (y>0) return 3.14/2; else
if (y<0) return 3.14*3/2; else
return 0;
}
}
void sw(double *a,double *b)
{
double t=*a; *a=*b; *b=t;
}
void qs(int left,int right)
{
int i,j; double p;
i=left; j=right; p=h[(i+j)/2];
while (i<j)
{
while (h[i]<p) i++;
while (h[j]>p) j--;
if (i<=j) {sw(&h[i],&h[j]);sw(&y[i],&y[j]);sw(&y[i],&y[j]); i++; j--;}
}
if (i<right) qs(i,right);
if (j>left) qs(left,j);
}
double dist(double x1,double y1,double x2,double y2)
{
return sqrt(pow(abs(x1-x2),2)+pow(abs(y1-y2),2));
}
int caut_bin(int i,int j,int left,int right)
{
int p;
double a,b,c;
if (left==right) return 0; else
{
p=(left+right)/2;
a=dist(x[i],y[i],x[j],y[j]);
b=dist(x[i],y[i],x[p],y[p]);
c=dist(x[p],y[p],x[j],y[j]);
if (b==c && b==a) return 1; else
if (b>p) caut_bin(i,j,left,p); else caut_bin(i,j,p+1,right);
}
}
void init()
{
int i,m; double px,py;
for (i=1; i<=n; i++) scanf("%f%f",&x[i],&y[i]);
px=x[1]; py=y[1];
for (i=2; i<=n; i++)
if (py>y[i]) { py=y[i]; px=y[i];}
for (i=1; i<=n; i++) { m=polar(x[i]-px,y[i]-py)*1000; h[i]=m/1000.0; }
}
int main()
{
int k,i,j,c; double a,b,d;
freopen("triang.in","r",stdin);
freopen("triang.out","w",stdout);
scanf("%i",&n);
init();
qs(1,n);
k=0;
for (i=1; i<=n-2; i++)
for (j=i+1; j<=n-1; j++)
{
k=k+caut_bin(i,j,j+1,n);
}
printf("%i",k);
return 0;
}