program ABC163_E
  integer,allocatable::A(:),M(:)
  read(*,*)N
  allocate(A(N),M(N-1))
 M=1
  do i=1,N-1
     do j=i+1,N
        if(A(j)*(j-i)>M) then
           M(i)=A(j)*(j-i)
           K=j
        end if
     end do
     A(K)=0
  end do
  write(*,*)sum(M)
end program ABC163_E