Calculate Fibonachi

/*
   This program calculate Fibonachi number serie:
   1,1,2,3,5,8,13,21,34...
   each number is the sum of the previous two numbers: 8=5+3, 5=3+2...

   Gabby Shimoni, December 2018
*/

long firstNum = 1;
long secondNum = 1;
long sum;
void setup() {
  Serial.begin(9600);
  sum = firstNum + secondNum;
  Serial.println(firstNum);
  Serial.println(secondNum);
  Serial.println(sum);
}

void loop() {
  firstNum = secondNum;
  secondNum = sum;
  sum = firstNum + secondNum;
  Serial.println(sum);
  delay(200);
}