boolean s1;
 boolean s2;
 boolean s3;
 boolean s4;

void setup() {
pinMode(2, OUTPUT);//buzzer
pinMode(4, INPUT_PULLUP);//s1
pinMode(8, INPUT_PULLUP);//s2
pinMode(5, INPUT_PULLUP);//s3
pinMode(6, INPUT_PULLUP);//s4
}
void loop()
{
  s1=digitalRead(4);
  s2= digitalRead(8);
  s3=digitalRead(5);
  s4=digitalRead(6);
  if(s1==LOW)
  {
    tone(2,261);
    delay(500);
    noTone(2);
  }

 if(s2==LOW)
{
tone(2, 294); // 2- buzer pin, 294- value of tone D4
delay(500);
noTone(2);
}
if(s3==LOW)
{
tone(2, 330); // 2- buzer pin, 330- value of tone E4
delay(500);
noTone(2);
}
if(s4==LOW)
{
tone(2, 349); // 2- buzer pin, 349- value of tone f4
delay(500);
noTone(2);
}

}