int bot = 4;
int led =  2;
int x = 0;

void setup()
{
  pinMode(led, OUTPUT);
  pinMode(bot, INPUT);
}

void loop()
{
  int stato = digitalRead(bot);
  if (stato == HIGH and x == 0)
  {
    digitalWrite(led, HIGH);
    x = 1;
  }
  else if (stato == HIGH and x == 1)
  {
    digitalWrite(led, LOW);
    x = 0;
    return;
  }
}