GPIO-IDR reads 1 value from input always(pull down and pull up too but there is no input)

Hi.I have some problem with Nucleo stm32f030r8.
I make a led blinking application.I make porta_0 as output and portb_0 as input and i make portb_0 pull down mode
I want that  when portb_0 being  1 level porta_0 turn to 1 level and led torn on but i have problem that i always read 1 value from idr for portb_0

It only works when i connect portb_0 to ground then led turns off 

I dont know why ?))

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