Small Mirela is in love with the hexagon. She loves to draw them in a circle, and notes that in each following round of the draft, which has six hexagonal rather than in previous. Mirela first draft of a hexagon, then around him, six new and continues to draw new hexagonal some of those who had already draw. In the first step, the draft is only one hexagon, and in each next step line layer of hexagonal drawn before.

After Mirela make N steps of drawing, you know What is the total hexagonal drawing.

INPUT:
Natural number N (1 ≤ N ≤ 70) - the number of drawing steps.

OUTPUT:
Total number of drawn hexagonal.

Example: 1.

Example: 2.