int btn;
int past_state;
void setup() {
  // put your setup code here, to run once:
  pinMode(3, INPUT_PULLUP);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  past_state=0;
}

void loop() {
  // put your main code here, to run repeatedly:
  btn=digitalRead(3);

  if(btn == 0){   //turn on red led
    if(past_state==0){
      digitalWrite(4, HIGH);
      past_state++;
    }
    else if(past_state==1){     //turn on green led
      digitalWrite(4, LOW);
      digitalWrite(5, HIGH);
      past_state++;
    }
    else if(past_state==2){      //turn on blue led
      digitalWrite(5, LOW);
      digitalWrite(6, HIGH);
      past_state++;
    }
    else if(past_state==3){      //turn on all leds
      digitalWrite(4, HIGH);
      digitalWrite(5, HIGH);
      past_state++;
    }
    else if(past_state==4){      //turn on blue led
      digitalWrite(4, LOW);
      digitalWrite(5, LOW);
      digitalWrite(6, LOW);
      past_state = 0;
    }
  }
  delay((100));

}