N = int(input())
XY = []
for i in range(N):
    XY.append(list(map(int,input().split())))

XYD = []
for i in range(N):
    for j in range(i+1,N):
        XYD.append([i,j,(XY[i][0]-XY[j][0])**2+(XY[i][1]-XY[j][1])**2])

XYD = sorted(XYD, key=lambda x: x[2])
cnt = 0
B = [False]*N
for i,j,d in XYD:
    if B[i]==False and B[j]==False:
        if i==0:
            cnt+=1
            B[j]=True
        else:
            B[i]=True
            B[j]=True
print(cnt)