n = int(input())
z = [list(map(int,input().split())) for _ in range(n)]

dis2 = []

for i in range(n):
    for j in range(i+1,n):
        d = (z[i][0] - z[j][0])**2 + (z[i][1] - z[j][1])**2
        dis2.append([i,j,d])
        
not_exist = set([])
dis2.sort(key= lambda val : val[2])
ans = 0

for i, j, dis in dis2:
    if i in not_exist or j in not_exist:
        pass
    elif i == 0:
        not_exist.add(j)
        ans += 1
    else:
        not_exist.add(i)
        not_exist.add(j)
        
print(ans)