#include <avr/io.h>           // this contains all the IO port definitions
#include <util/delay.h>

#define DELAY 625             // 625ms * 32 = 20 seconds

int main (void) {
  DDRB = 0x1F;                // output: 0, 1, 2, 3, 4

  while (1) {
    for (int i = 0; i < 32; i++) {
      PORTB = i;
      _delay_ms(DELAY);
    }
  }

  return 0;
}