#define S1 2
#define S2 3
#define S3 4
#define S4 5

int counter1, counter2;
int PR1, PR2, PR3, PR4; //PR = Press Realease

void setup() {
  pinMode(S1, INPUT_PULLUP);
  pinMode(S2, INPUT_PULLUP);
  pinMode(S3, INPUT_PULLUP);
  pinMode(S4, INPUT_PULLUP);

  Serial.begin(9600);
}

void loop() {
  //  COUNTER 1_UP
  if (PR1 == 0 && digitalRead(S1) == 0 && counter1 < 20){
    PR1 = 1;
  }
  if (PR1 == 1 && digitalRead(S1) == 1){
    counter1++;
    PR1 = 0;
  }
  //  COUNTER 1_DOWN
  if (PR2 == 0 && digitalRead(S2) == 0 && counter1 > 0 && counter2 == 0){
    PR2 = 1;
  }
  if (PR2 == 1 && digitalRead(S2) == 1){
    counter1--;
    PR2 = 0;
  }



  //  COUNTER 2_UP
  if (PR3 == 0 && digitalRead(S3) == 0 && counter2 < 20 && counter1 == 20){
    PR3 = 1;
    }
  if (PR3 == 1 && digitalRead(S3) == 1){
    counter2++;
    PR3 = 0;
  }
  //  COUNTER 2_DOWN
  if (PR4 == 0 && digitalRead(S4) == 0 && counter2 > 0){
    PR4 = 1;
  }
  if (PR4 == 1 && digitalRead(S4) == 1){
    counter2--;
    PR4 = 0;
  }

 //  SERIAL MONITOR
 Serial.print("Counter1: ");
 Serial.print(counter1);
 Serial.print(" | ");
 Serial.print("Counter2: "); 
 Serial.print(counter2);
 Serial.println();
    
}