void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(5, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(18, OUTPUT);
  pinMode(19, OUTPUT);

}

void loop() {
  if(digitalRead(5)==LOW) {
    digitalWrite(5, HIGH);
    digitalWrite(4, LOW);
    digitalWrite(18, HIGH);
    digitalWrite(19, LOW);
  } else if(digitalRead(4)==LOW) {
    digitalWrite(5, LOW);
    digitalWrite(4, HIGH);
    digitalWrite(18, LOW);
    digitalWrite(19, HIGH);
  } 
  
  delay(500); // this speeds up the simulation
}