fib(n){
	if(n<=0){
		return 0;
	}
	int i = n-1;
	a = 1;
	b = 0;
	c = 1;
	d = 0;
	aux = 0;
	while(i>0){
		if(i%2==0){
			aux = a;
			a = d*b + c*a;
			b = d*(b + aux) + c*b;
			aux = c;
		}
		c = c*c + d*d;
		d = d*(2*aux + d);
		i/=i;
	}
	return a+b;
}