output_description: Print the number of bouquets that Akari can make, modulo (10^9 + 7). (If there
  are no such bouquets, print `0`.)
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      n a b
attempt: mod = 10**9 + 7
  n, a, b = map(int, input().split())
  pows = [2]
  for _ in range(40):
      pows.append((pows[-1] ** 2) % mod)
  ans = 1
  flag = format(n, "b")
  if len(flag) < 31:
      flag = (31 - len(flag)) * "0" + flag
  flag = flag[::-1]
  for i in range(31):
      if flag[i] == "1":
          ans *= pows[i]
          ans %= mod
  ans -= 1
  rfacts = [pow(1, mod - 2, mod) % mod, pow(1, mod - 2, mod) % mod]
  for i in range(2, 2 * (10**5) + 1):
      rfacts.append((rfacts[-1] * pow(i, mod - 2, mod)) % mod)
  if n <= 2 * 10**5:
      fact = 1
      for i in range(2, n + 1):
          fact *= i
          fact %= mod
      ans -= (fact * rfacts[a] * rfacts[n - a]) % mod
      ans %= mod
      ans -= (fact * rfacts[b] * rfacts[n - b]) % mod
      ans %= mod
  else:
      fact1 = 1
      for i in range(n, n - a, -1):
          fact1 *= i
          fact1 %= mod
      ans -= (fact1 * rfacts[a]) % mod
      ans %= mod
      fact2 = 1
      for i in range(n, n - b, -1):
          fact2 *= i
          fact2 %= mod
      ans -= (fact2 * rfacts[b]) % mod
      ans %= mod
  print(ans)
  
problem_description: Statement
  
  Akari has n kinds of flowers, one of each kind.
  
  She is going to choose one or more of these flowers to make a bouquet.
  
  However, she hates two numbers a and b, so the number of flowers in the
  bouquet cannot be a or b.
  
  How many different bouquets are there that Akari can make?
  
  Find the count modulo (10^9 + 7).
  
  Here, two bouquets are considered different when there is a flower that is
  used in one of the bouquets but not in the other bouquet.
samples: [{"input": "4 1 3", "output": "7\n    \n\nIn this case, Akari can choose 2 or 4 flowers to make the bouquet.\n\nThere are 6 ways to choose 2 out of the 4 flowers, and 1 way to choose 4, so\nthere are a total of 7 different bouquets that Akari can make.\n\n* * *"}, {"input": "1000000000 141421 173205", "output": "34076506\n    \n\nPrint the count modulo (10^9 + 7)."}]