void setup() {
  // put your setup code here, to run once:
  DDRC &= 0b11111000;
  PORTC |= 0b00000111; // A0-A2 as PullUp
  // pinMode(A0, INPUT_PULLUP);

}

void loop() {
  // put your main code here, to run repeatedly:
  if((PINC & 0b00000001) == 0) {  // Test bit 0 only
    PORTB |= 0b00100000;          // BUILTIN_LED pin 13 On
  } else {
    PORTB &= ~0b00100000;         // BUILTIN_LED pin 13 Off
  }
/* or this way
  if(PINC & 0b00000001) {   // Test bit 0 only
    PORTB &= ~0b00100000;   // BUILTIN_LED pin 13 Off
  } else {
    PORTB |= 0b00100000;    // BUILTIN_LED pin 13 On
  }
*/
}