# 接受输入周长
x = float(input())
# 圆周率3.14
p = 3.14
# 计算半径
r = x / (2 * p)
# 计算面积
s = r * r * p
print('%.2f' % s)

/**************************************************************
	Problem: 1337
	User: admin
	Language: Python
	Result: Accepted
	Time:91 ms
	Memory:34244 kb
****************************************************************/