int ledpin1 = 19;
int ledpin2 = 21;

void setup() {
  // put your setup code here, to run once:
  pinMode(ledpin1, OUTPUT);
  pinMode(ledpin2, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(ledpin1, HIGH);
  digitalWrite(ledpin2, LOW);
  delay(1000);

  digitalWrite(ledpin1, LOW);
  digitalWrite(ledpin2, HIGH);
  delay(1000);
}