import numpy as np

N=int(input())
S=np.full((N,2),0)

for i in range(N):
    A,B=map(int,input().split())
    S[i][0]=A
    S[i][1]=B
    
    
count=0

while N!=1:
    tmp=10**18
    for i in range(N):
        tmpx1=S[i][0]
        tmpy1=S[i][1]
        for j in range(N):
            if i!=j:
                tmpx2=S[j][0]
                tmpy2=S[j][1]
                
                if (tmpx2-tmpx1)**2+(tmpy2-tmpy1)**2<tmp:
                    tmp=(tmpx2-tmpx1)**2+(tmpy2-tmpy1)**2
                    tmp1=i
                    tmp2=j
    #print("tmp",tmp,tmp1,tmp2)
    if tmp1==0:
        N-=1
        S=np.delete(S,tmp2,0)
        count+=1
    elif tmp2==0:
        N-=1
        S=np.delete(S,tmp1,0)
        count+=1
    else:
        N-=2
        #print("mohu2")
        S=np.delete(S,max(tmp1,tmp2),0)
        S=np.delete(S,min(tmp1,tmp2),0)
    #print(S)
    #print("mohu")
print(count)