program C176
    implicit none
    integer(4) :: N
    integer(4), allocatable :: A(:)
    integer(4) :: i, step

    read(5,*) N
    allocate(A(N))
    read(5,*) (A(i), i = 1, N)

    step = 0
    do i = 2, N
        if (A(i-1)>A(i)) then 
            step = step + A(i-1) - A(i)
            A(i) = A(i-1)
        end if


    end do

    write(6,*) step
    
end program C176