#include "avr/io.h"
  #include "avr/interrupt.h"
  
  int main ()
  {
    ddrc = 1<<3;  
    portd = 1<<2;    
    gicr = (1<<int0);  
    sei ();      
  
    while (1);      
  }
  
  isr (int0_vect)      
  {
    portc ^= (1<<3);    
  }