const int button1 = 8; 
  const int button2 = 9; 
  const int button3 = 10; 
  const int button4 = 11; 
  int oku; 
   
  void setup() { 
    pinMode(button1, INPUT); 
    pinMode(button2, INPUT); 
    pinMode(button3, INPUT); 
    pinMode(button4, INPUT); 
    Serial.begin(9600); 
   
  } 
  void loop() { 
    if(Serial.available()){ 
      oku = Serial.read(); 
      if(digitalRead(button1) == HIGH && oku == '1'){ 
        Serial.println("1"); 
        } 
        else if(digitalRead(button2) == HIGH && oku == '2'){ 
        Serial.println("2"); 
        } 
        else if(digitalRead(button3) == HIGH && oku == '3'){ 
        Serial.println("3"); 
        } 
        else if(digitalRead(button4) == HIGH && oku == '4'){ 
        Serial.println("4"); 
        } 
       
      } 
   
  }