int cislo = 0;
bool x = true;

void setup() {
pinMode(12, INPUT);
digitalWrite(12, HIGH);
Serial.begin(9600);
}

void loop() {
if(digitalRead(12)== LOW && x == true)
{
  cislo ++;
  Serial.println(cislo);
  x = false;
}

if(digitalRead(12)== HIGH && x == false)
  x = true;
}