Attiny25 binary counter

counter.c

#include <avr/io.h>

int main(void) {
  PORTB = 0;
  DDRB = 0b1111;
  uint8_t counter = 0;
  uint8_t input=0;
  uint8_t previous_input=0;
  while(1) {
    input = PINB & (1<<PINB4);
    if ((input == 0) && (previous_input != input)) {
      PORTB = (counter>>1) & 0b1111;
      counter++;
    }
    previous_input = input;
  }
  return 0;
}