n=int(input())
pos=[list(map(int,input().split())) for _ in range(n)]
dist=[]
for i in range(n):
    x1,y1=pos[i]
    for j in range(i+1,n):
        x2,y2=pos[j]
        d=((x1-x2)**2+(y1-y2)**2)**0.5
        dist.append((d,i,j))
dist=sorted(dist,key=lambda x:x[0])
used=set()
ans=0
for _,i,j in dist:
    if i==0:
        if j in used:
            continue
        else:
            ans+=1
            used.add(j)
    else:
        if i in used or j in used:
            continue
        else:
            used.add(i)
            used.add(j)
print(ans)