import sys
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())


N = I()
xy = [tuple(MI()) for _ in range(N)]
dist = []
for i in range(N-1):
    x0,y0 = xy[i]
    for j in range(i+1,N):
        x1,y1 = xy[j]
        dist.append(((x0-x1)**2+(y0-y1)**2,i,j))

dist.sort()
left = [1]*N

ans = 0
for d,i,j in dist:
    if left[i] == 0 or left[j] == 0:
        continue
    if i == 0:
        ans += 1
        left[j] = 0
    else:
        left[i] = 0
        left[j] = 0

print(ans)