program prob3
    implicit none
    integer::n, m, d
    real(8)::ans
    read(*,*) n, m, d
    if(d == 0) then
        ans = dble(1)*dble(m-1) / dble(n)
    else
        ans = dble(2)*dble(n-d)*dble(m-1) / dble(n)**2
    end if
    write(*,*) ans
    stop
end program