Cells in a circle#129
On a sheet of graph paper with unit squares, a circle of radius is drawn so that its center is at the intersection of grid lines. Determine how many complete cells (unit squares) are entirely contained within the circle.
The only line contains one integer (0 \leq R \leq 1000), the radius of the circle.
Output a single integer: the number of unit squares entirely contained within the circle.
Example 1