C :

#include <stdio.h>
void main()

{
	double i,r,s,p=3.14;
	scanf("%lf",&i);
	r=i/2.0/p;
	s=3.14*r*r; 
	printf("%.2f",s);
 }

C++ :

#include<bits/stdc++.h>
using namespace std;

int main(){
	double s,c,r,pi = 3.14;
	cin>>c;
	r = c / (2 * pi);
	s = pi * r * r;
	cout<<fixed<<setprecision(2)<<s<<endl;
	 
    return 0;
}

Pascal :

var
  c,s:real;
begin
  read(c);
  s:=c/6.28;
  s:=s*s*3.14;
  write(s:0:2);
end.

Java :

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double x = sc.nextDouble();
		double pi = 3.14;
		//定义面积为s
		double s ;
		double r = x /(2*pi);
		s = pi * r * r;
		System.out.printf("%.2f",s);
	}
}

Python :

# 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)