module mdl

contains
    function calc(c,trg)
        integer*8::calc,c(:),trg
        calc=0
        do i=1,size(c)
            calc=calc+abs(c(i)-trg)
        end do
    end function
end module


program main
    use mdl
    implicit none
    integer*8::b,n,tot=0,i,j,k,s,t,ans
    integer*8,allocatable::c(:)
    read*,b
    read*,n
    allocate(c(n))
    tot=b
    do i=1,n
        read*,c(i)
        tot=tot+c(i)
    end do
    s=0
    t=tot/n
    do while(t-s>2)
        i=(2*s+t)/3
        j=(s+2*t)/3
        if(calc(c,i)<calc(c,j))then
            t=j
        else
            s=i
        end if
    end do
    ans=calc(c,s)
    do i=s,t
        ans=min(ans,calc(c,i))
    end do
    print*,ans
end program