Problem:
Score : 400 points

Problem 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.

Constraints

All values in input are integers.

2 \leq n \leq 10^9

1 \leq a < b \leq \textrm{min}(n, 2 \times 10^5)

Input

Input is given from Standard Input in the following format:

n a b

Output

Print the number of bouquets that Akari can make, modulo (10^9 + 7). (If there are no such bouquets, print 0.)

Sample Input 1

4 1 3

Sample Output 1

7

In this case, Akari can choose 2 or 4 flowers to make the bouquet.

There are 6 ways to choose 2 out of the 4 flowers, and 1 way to choose 4, so there are a total of 7 different bouquets that Akari can make.

Sample Input 2

1000000000 141421 173205

Sample Output 2

34076506

Print the count modulo (10^9 + 7).

Solution in Fortran (gfortran v4.8.4) (judge verdict: Runtime Error)

module Factwithmod
  implicit none
  integer(16),allocatable,dimension(:)::Kaijo,comb
  contains
subroutine initiationFactorial(maxnum,mo)
  implicit none
  integer(16)::maxnum
  integer(16)::mo
  integer(16)::i

  allocate(Kaijo(0:maxnum))
  Kaijo(0)=1
  do i=1,maxnum
    Kaijo(i)=mod(Kaijo(i-1)*i,mo)
  end do
end subroutine

subroutine combination(n,maxnum,l)
implicit none
integer(16),intent(in)::n,maxnum,l
integer(16)::i
allocate(comb(maxnum))
comb(1)=N
do i=2,maxnum
    comb(i)=comb(i-1)*(N-i+1)*inv(i,l)
    comb(i)=mod(comb(i),l)
end do
end subroutine

function inv(K,L)
integer(16),intent(in)::k,l
integer(16) l2,y
integer(16) inv
inv=1
l2=l-2
y=k
do
  if(mod(l2,2)==1)inv=mod(inv*y,l)
  y=mod(y*y,l)
  l2=l2/2
  if(l2==0)exit
end do
end function

function permutation(n,k,mo)
implicit none
  integer(16)::n,k
  integer(16)::mo,permutation
  permutation=mod(Kaijo(N)*inv(Kaijo(N-K),mo),mo)
end function
end module Factwithmod
program ABC156b
    use Factwithmod
    implicit none
    integer(16)::N
    integer(16)::a,b
    integer(16)::mo=10**9+7
    integer(16)::allc
    integer(16)::ans
    read*,N,a,b
    call initiationFactorial(N,mo)
    call combination(N,b,mo)
    allc=power_func(2_16,N,mo)-1_16
    ans=allc-comb(a)-comb(b)
    ans=mod(ans,mo)
    if(ans<0)ans=ans+mo
    print"(i0)",ans
contains
integer(16) function power_func(a,n,mo)
    integer(16)::a,n,mo
    integer(16)::l2,y
    power_func=1
    l2=N
    y=a
    do
        if(mod(l2,2)==1)power_func=mod(power_func*y,mo)
        y=mod(y*y,mo)
        l2=l2/2
        if(l2==0)exit
    end do
end function power_func
end program ABC156b