Theatre Square

用 $ a \times a$ 的石板覆盖 $n \times m $ 的长方形广场，允许石板覆盖的区域超出广场，不允许打破石板，石板的两侧应平行于广场两侧，要求覆盖完广场所需的石板数量最少是多少。 感谢 @Loner_Knowledge 贡献翻译。

Theatre Square in the capital city of Berland has a rectangular shape with the size $ n×m $ meters. On the occasion of the city's anniversary, a decision was taken to pave the Square with square granite flagstones. Each flagstone is of the size $ a×a $ . What is the least number of flagstones needed to pave the Square? It's allowed to cover the surface larger than the Theatre Square, but the Square has to be covered. It's not allowed to break the flagstones. The sides of flagstones should be parallel to the sides of the Square.

The input contains three positive integer numbers in the first line: $ n,m $ and $ a $ ( $ 1\leq n,m,a\leq10^{9} $ ).

Write the needed number of flagstones.

6 6 4

4

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