bool ready = false;
bool writy = true;
long timestamp = 0;
long timestamp_other = 0;
long timestamp_new = 0;
long transittime = 0;
long receivedelay = 0;

void setup() {
  Serial.begin(57600);
  delay(5000);
}
void loop() {
 

  if (writy) {
    timestamp = millis();
    Serial.println(timestamp);
    ready = true;
    writy = false;
  }
  if (Serial.available()) {
    if(ready){
      receivedelay = millis();
      timestamp_other = Serial.parseInt();
      receivedelay =  millis()-receivedelay;
      transittime = millis()-timestamp;
      timestamp_new =  timestamp_other + transittime/2 - receivedelay;
      Serial.println(timestamp_new);
      Serial.println(timestamp_other);
      Serial.println(transittime);
      Serial.println(receivedelay);
      ready = false;
    }

  }

}