#define pBa 21
#define pBb 22
#define pBc 23
#define led 0

bool y;

void setup(){
  pinMode(led, OUTPUT);
  pinMode(pBa, INPUT);
  pinMode(pBb, INPUT);
  pinMode(pBc, INPUT);
}

void loop(){
  y=digitalRead(pBa) && 
  digitalRead(pBb) && 
  digitalRead(pBc);
  digitalWrite(led, y);
}