aspect optimization  // also prevents overflow...
{
    /* fast fibonacci */
    int[] mmult(int[] A, int[] B) // 2x2 matrix multiplication
    {   int[] C = new int[4];
	C[0] = (A[0]*B[0] + A[1]*B[2]);
	C[1] = (A[0]*B[1] + A[1]*B[3]);
	C[2] = (A[2]*B[0] + A[3]*B[2]);
        C[3] = (A[2]*B[1] + A[3]*B[3]);
	return C;
    }
   
    int around(int n) : call(int base+.fib(int)) && args(n)
    {
	if (n<3) return 1;
	int[] AX = {1,1,1,0};  // fibonacci matrix (in 1D)
	int[] Binfact = {1,1,1,0};
	n-=2;
	while (n>0)
	    {
		if (n%2==1) AX = mmult(AX,Binfact);
		Binfact = mmult(Binfact,Binfact);
		n = n/2;  // right shift
	    }
	return AX[0];
    }// around advice replaces inefficient fibonacci call
    
}//optimization