说明

We need a programmer to help us for some projects. If you show us that you or one of your friends is able to program, you can pass the first hurdle. I will give you a problem to solve. Since this is the first hurdle, it is very simple.

We all know that the simplest program is the “Hello World!” program. This is a problem just as simple as the “Hello World!”. This is a problem called AC (Area of a Cake).

Angel is a very beautiful girl, but she does not understand any mathematical knowledge. Angel likes to use various ovens to make some cakes. The ovens are square (whose width equal to length), while the cakes are round or circle. That is to say, the maximal area of cake is related with the width of the oven, that is S=PI*R^2. Angel can easy find the width of oven from specification, but here comes the problem: What’s the maximal area of the cake? Can you help her? Of course, you should firstly calculate PI with tan(PI/4)=1.

输入格式

The input consists of several test cases.

Each line contains one integer R (1<=R<=10000), which represents half of the width of the oven.

输出格式

For each case, print the area of a cake, and output the result in a single line. Your output format should imitate the sample output, which rounds to seven figures after the decimal point.

4

50.2654825

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