import sys

def side(p1,p2):

  global D

  y1,x1=p1

  y2,x2=p2

  dy=y2-y1

  dx=x2-x1

  for p3 in D[::-1]:

    if p1==p3 or p2==p3:continue

    y3,x3=p3

    if (x3-x1)*dy-dx*(y3-y1)<0:return 0

  else:return 1



while 1:

  n=eval(input())

  if n==0:break

  D=sorted([list(eval(input())) for i in range(n)])

  p=p1=D[0]

  D1=D[:]

  while True:

    for p2 in D1:

      if p1!=p2 and side(p1,p2):break

    p1=p2

    D1.remove(p2)

    if p2==p:break

  print(len(D1))
import sys

def side(p1,p2):

  global D

  y1,x1=p1

  y2,x2=p2

  dy=y2-y1

  dx=x2-x1

  for p3 in D[::-1]:

    if p1==p3 or p2==p3:continue

    if (p3[1]-x1)*dy-dx*(p3[0]-y1)<0:return 0

  else:return 1



while 1:

  n=eval(input())

  if n==0:break

  D=sorted([list(eval(input())) for i in range(n)])

  p=p1=D[0]

  D1=D[:]

  while True:

    for p2 in D1:

      if p1!=p2 and side(p1,p2):break

    p1=p2

    D1.remove(p2)

    if p2==p:break

  print(len(D1))
import sys


def side(p1, p2):
    global D
    y1, x1 = p1
    y2, x2 = p2
    dy = y2 - y1
    dx = x2 - x1
    for p3 in D[::-1]:
        if p1 == p3 or p2 == p3:
            continue
        y3, x3 = p3
        if (x3 - x1) * dy - dx * (y3 - y1) < 0:
            return 0
    else:
        return 1


while 1:
    n = eval(input())
    if n == 0:
        break
    D = sorted([list(eval(input())) for i in range(n)])
    p = p1 = D[0]
    D1 = D[:]
    while True:
        for p2 in D1:
            if p1 != p2 and side(p1, p2):
                break
        p1 = p2
        D1.remove(p2)
        if p2 == p:
            break
    print(len(D1))

import sys


def side(p1, p2):
    global D
    y1, x1 = p1
    y2, x2 = p2
    dy = y2 - y1
    dx = x2 - x1
    for p3 in D[::-1]:
        if p1 == p3 or p2 == p3:
            continue
        if (p3[1] - x1) * dy - dx * (p3[0] - y1) < 0:
            return 0
    else:
        return 1


while 1:
    n = eval(input())
    if n == 0:
        break
    D = sorted([list(eval(input())) for i in range(n)])
    p = p1 = D[0]
    D1 = D[:]
    while True:
        for p2 in D1:
            if p1 != p2 and side(p1, p2):
                break
        p1 = p2
        D1.remove(p2)
        if p2 == p:
            break
    print(len(D1))

-        y3, x3 = p3 -        if (x3 - x1) * dy - dx * (y3 - y1) < 0: +        if (p3[1] - x1) * dy - dx * (p3[0] - y1) < 0: