题解 | #牛牛的圆#
牛牛的圆
https://www.nowcoder.com/practice/75a202e826d048a39824ec694b5ce7e3
using System;
public class Program {
public static void Main() {
string s = Console.ReadLine();
Console.WriteLine(3.14*Math.Pow(Convert.ToInt32(s), 2));
}
}
