问题描述



给定圆的半径r，求圆的面积。



输入格式



输入包含一个整数r，表示圆的半径。



输出格式



输出一行，包含一个实数，四舍五入保留小数点后7位，表示圆的面积。



说明：在本题中，输入是一个整数，但是输出是一个实数。



对于实数输出的问题，请一定看清楚实数输出的要求，比如本题中要求保留小数点后7位，则你的程序必须严格的输出7位小数，输出过多或者过少的小数位数都是不行的，都会被认为错误。



实数输出的问题如果没有特别说明，舍入都是按四舍五入进行。



样例输入



4



样例输出



50.2654825



数据规模与约定



1 <= r <= 10000。



提示



本题对精度要求较高，请注意π的值应该取较精确的值。你可以使用常量来表示π，比如PI=3.14159265358979323，也可以使用数学公式来求π，比如PI=atan(1.0)*4。-Problem descr iption

A given circle radius r, and the area of a circle.

Input format

Input contains an integer r, said the radius of the circle.

The output format

Output a line contains a real number, rounded after the decimal point 7, said the area of a circle.

Note: in the ontology, the input is an integer, but the output is a real number.

Answer to the question of the real output please see real output requirements, such as the subject of seven after decimal point, is the output of your application must be strictly 7 decimal places, the output of decimal digits too little or too much is not enough, will be considered.

The problem of real output if there are no special instructions, rounding is each round.

The sample input

4

Sample output

50.2654825

The data scale and conventions

1 < = r < = 10000.

prompt

Subject to the precision demand is higher, please pay attention to the value of PI should take more accurate values. You can use a constant to represent the PI