n=int(input())
xy=[]
x0,y0=map(int,input().split())
for i in range(n-1):
    x,y=map(int,input().split())
    x-=x0
    y-=y0
    xy.append([x**2+y**2,x,y])
ans=0
xy.sort()
for i in range(n-1):
    xi,yi=xy[i][1],xy[i][2]
    dis=10**12
    for j in range(n-1):
        if j!=i:
            dis=min(dis,(xy[j][1]-xi)**2+(xy[j][2]-yi)**2)

    if dis>xi**2+yi**2:
        ans+=1
        xy[i]=[10**12,10**12,10**12]
print(ans)