void setup() {
  Serial.begin(9600);
  pinMode(13, OUTPUT);
}

void loop() {
  int k1 = analogRead(A3);
  int k2 = analogRead(A2);
  int k3 = analogRead(A1);
  int k4 = analogRead(A0);
  Serial.print("k1 = ");
  Serial.println(k1);
  Serial.print("k2 = ");
  Serial.println(k2);
  Serial.print("k3 = ");
  Serial.println(k3);
  Serial.print("k4 = ");
  Serial.println(k4);

  if(k1 >= 100 && k1 <= 200 && k2 >= 500 && k2 <= 550 && k3 >= 800 && k3 <= 900 && k4 <= 50)
    digitalWrite(13, HIGH);
  else
    digitalWrite(13, LOW);

  delay(1000);
}