int redpin = 18;
int greenpin = 19;
int Button = 21;
int data21;

void setup() {

  Serial.begin(115200);
  pinMode(Button, INPUT_PULLUP);
  pinMode(greenpin, OUTPUT);
  pinMode(redpin, OUTPUT);
}

void loop() {
  //red=18 green = 19
 delay(1000);
 data21 = digitalRead(21);
 Serial.println("pin 21 = " + String(data21));

 if(digitalRead(Button) == 0){
  digitalWrite(redpin, HIGH);
  digitalWrite(greenpin, LOW);
  
 }if (digitalRead(Button) == 1){
  digitalWrite(redpin, LOW);
  digitalWrite(greenpin, HIGH);
 }
 }