output_description: Print the minimum possible number of indices i such that A_i and C_i are
  different, for a sequence C_1, C_2, ..., C_{N} that satisfies the conditions.
  If such a sequence C_1, C_2, ..., C_{N} cannot be constructed, print -1.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      A_1 A_2 ... A_{N}
      B_1 B_2 ... B_{N}
attempt: n = int(input())
  s = list(map(int, input().split()))
  dum = s[0]
  count = 0
  for i in s:
      if i <= dum:
          count += 1
      dum = min(dum, i)
  print(count)
  
problem_description: Statement
  
  A university student, Takahashi, has to take N examinations and pass all of
  them. Currently, his _readiness_ for the i-th examination is A_{i}, and
  according to his investigation, it is known that he needs readiness of at
  least B_{i} in order to pass the i-th examination.
  
  Takahashi thinks that he may not be able to pass all the examinations, and he
  has decided to ask a magician, Aoki, to change the readiness for as few
  examinations as possible so that he can pass all of them, while not changing
  the total readiness.
  
  For Takahashi, find the minimum possible number of indices i such that A_i and
  C_i are different, for a sequence C_1, C_2, ..., C_{N} that satisfies the
  following conditions:
  
    * The sum of the sequence A_1, A_2, ..., A_{N} and the sum of the sequence C_1, C_2, ..., C_{N} are equal.
    * For every i, B_i \leq C_i holds.
  
  If such a sequence C_1, C_2, ..., C_{N} cannot be constructed, print -1.
samples: [{"input": "3\n    2 3 5\n    3 4 1", "output": "3\n    \n\n(A_1, A_2, A_3) = (2, 3, 5) and (B_1, B_2, B_3) = (3, 4, 1). If nothing is\ndone, he cannot pass the first and second exams. The minimum possible number\nof indices i such that A_i and C_i are different, 3, is achieved when:\n\n  * (C_1, C_2, C_3) = (3, 5, 2)\n\n* * *"}, {"input": "3\n    2 3 3\n    2 2 1", "output": "0\n    \n\nIn this case, he has to do nothing in order to pass all the exams.\n\n* * *"}, {"input": "3\n    17 7 1\n    25 6 14", "output": "-1\n    \n\nIn this case, no matter what is done, he cannot pass all the exams.\n\n* * *"}, {"input": "12\n    757232153 372327760 440075441 195848680 354974235 458054863 463477172 740174259 615762794 632963102 529866931 64991604\n    74164189 98239366 465611891 362739947 147060907 118867039 63189252 78303147 501410831 110823640 122948912 572905212", "output": "5"}]