#define pin1 6
#define pin2 5
#define pin3 1
int freq=0;
int T=0;
void setup()
{
  DDRB= 0x00; //input config
  DDRC= 0xFF; //output config
}
void choiceOfFreq()
{
  PINB= 0xFF; //taking input
  if((PINB & 0x60)==0x00)
  freq=50;
  if((PINB & 0x60)==0x20)
  freq=100;
  if((PINB & 0x60)==0x40)
  freq=200;
  if((PINB & 0x60)==0x60)
  freq=250;
  T=1000000/freq;
}
void loop()
{
  choiceOfFreq();
  PORTC |= (1<<pin3);
  delay(T/2);
  PORTC &= ~(1<<pin3);
  delay(T/2);
}