#include <stdio.h>
#include <math.h>

FILE *f,*g;
float point[1500][2];
int n,i,j,how;

int main(){
f=fopen("triang.in","r");
g=fopen("triang.out","w");
fscanf(f,"%d",&n);
for(i=0;i<n;i++){
  fscanf(f,"%f",&point[i][0]);
  fscanf(f,"%f",&point[i][1]);
}
for(i=0;i<n-2;i++)
  for(j=i+1;j<n;j++)
     if(
        sqrt((point[j-1][0]*point[j-1][0]-2*point[j-1][0]*point[i][0]+point[i][0]*point[i][0])+
            (point[j-1][1]*point[j-1][1]-2*point[j-1][1]*point[i][1]+point[i][1]*point[i][1])) &&

            sqrt((point[j][0]*point[j][0]-2*point[j][0]*point[i][0]+point[i][0]*point[i][0])+
            (point[j][1]*point[j][1]-2*point[j][1]*point[i][1]+point[i][1]*point[i][1]))       &&

            sqrt((point[j-1][0]*point[j-1][0]-2*point[j-1][0]*point[j][0]+point[j][0]*point[j ][0])+
            (point[j-1][1]*point[j-1][1]-2*point[j-1][1]*point[j][1]+point[j][1]*point[j][1]))
       ) how++;

fprintf(g,"%d\n",how);
fclose(g);
return 0;
}