interruption that works

int A, B, i=0;

void setup() {
  // put your setup code here, to run once:
  pinMode(4, INPUT);
  pinMode(3, INPUT);
  Serial.begin(38400);
  attachInterrupt(digitalPinToInterrupt(2), fn, CHANGE);
  attachInterrupt(digitalPinToInterrupt(3), fn, CHANGE);
}

void loop() {
  // put your main code here, to run repeatedly:


}

void fn(){
    int ia = i;


  if(A==B){
    if(A!=digitalRead(4)){
      i++;
      A = digitalRead(4);
    }
    if(B!=digitalRead(3)){
      i--;
      B = digitalRead(3);
    }
  }

  else{
    if(A!=digitalRead(4)){
      i--;
      A = digitalRead(4);
    }
    if(B!=digitalRead(3)){
      i++;
      B = digitalRead(3);
    }
  }

  if(i != ia){
  Serial.print("\n\n\n\n\n\n\n\n pulsos:");
  Serial.println(i);
}
}