n = int(input())
al = []
for i in range(n):
  a,b = map(int,input().split())
  al.append((a,b))
#次の順列を出力.もうなかったら-1を出します。
def Next_P(now):
  last_higher = -1
  nagasa = len(now)
  for i in range(nagasa-1):
    if now[i] < now[i+1]:
      last_higher = i
  if last_higher == -1:
    return -1
  else:
    last_higher_higher = -1
    for j in range(last_higher+1,nagasa):
      if now[last_higher] < now[j]:
        last_higher_higher = j
    now[last_higher],now[last_higher_higher] = now[last_higher_higher],now[last_higher]
    hanten = now[last_higher+1:]
    hanten = hanten[::-1]
    now = now[:last_higher+1] + hanten

    return now
now = list(range(n))
ans = 0
while now != -1:
  num = 0
  p = True
  for i in range(n):
    num = max(num,al[now[i]][0])
    if num > al[now[i]][1]:
      p = False
      break
  if p:
    ans += 1
  now = Next_P(now)
print(ans)