long  cislo = 0;

void setup() {
  DDRB |= 1<<5;
  PORTB |= 1<<5;
delay(50);
PORTB &= ~(1<<5);
PORTB |= 1<<5;
delay(50);
PORTB &= ~(1<<5);
  Serial.begin(9600);
  Serial.println("zadajte cislo:");
}

void loop() {
while( ! Serial.available() );
cislo = Serial.parseInt(); 
for(int i=0; i<cislo; i++){
PORTB |= 1<<5;
delay(50);
PORTB &= ~(1<<5);
delay(50);
}
bufferCleaner();

}
void bufferCleaner()
{
 delay(1);
 while(Serial.available())
 Serial.read();
}