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

FILE *f,*g;
float point[1500][2];
int n,i,j,how;
float x1,x2,x3;
float y,y2,y3;

int function(float a,float b, float c){
float precision=0.001;
if(
     ((a - precision )<b&&(a+precision)>b)&&
     ((a - precision )<c&&(a+precision)>c)) return 1;

return 0;
}

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+2;j<n;j++){
    x1=point[i][0];
    y=point[i][1];
    x2=point[j-1][0];
    y2=point[j-1][1];
    x3=point[j][0];
    y3=point[j][1];
    if(function(
        sqrt( (x2*x2-2*x2*x1+x1*x1)+(y2*y2-2*y2*y+y*y) ),
        sqrt( (x3*x3-2*x3*x1+x1*x1)+(y3*y3-2*y3*y+y*y) ),
        sqrt( (x2*x2-2*x2*x3+x3*x3)+(y2*y2-2*y2*y3+y3*y3) )
       )) how++;
   }
fprintf(g,"%d\n",how);
fclose(g);
return 0;
}