It's interesting that answer approaches to pi number without decimal point. If you'll increase r, answer becomes more and more precisely. For example: answer for r = 1e5 is 31416325412, but for r = 1e9 (although r < 1e5) is 3141592657589764752, when pi equals to 3.141592653 Anybody knows why it's happens?
Square of cirlce is Pi*r*r. Also it tends to some amount of little squares, because big cirlce is more bigger than one little square. Actually we have then amount of squares = pi*r*r on the big r. If r=10^k then pi*r*r=pi*10^2k=amount of squares Sorry for bad english=)