public class MatrixStack {
	int top = 0, stackSize = 20;
	Matrix3D stack[] = new Matrix3D[stackSize];

	public MatrixStack() {
		for (int i = 0; i < stackSize; i++)
			stack[i] = new Matrix3D();
	}

	public void push(Matrix3D m) {
		if (top < stackSize) {
			stack[top + 1].copy(m);
			top++;
		}
	}

	public void pop() {
		if (top > 0)
			--top;
	}

	public Matrix3D get() {
		return stack[top];
	}
}