C :

#include<stdio.h>
int main()
{
	double n,i,t=0,f,s=0;
	scanf("%lf",&n);
	f=1;
    for(i=1;i<=n;i++)
	{
		
		t=t+f*(2*i-1);
		s=s+1.0/t;
		f=-f;
	}
	printf("%.2lf\n",s);
	return 0;
}

C++ :

#include <iostream>
#include <stdio.h>
using namespace std;
int main()
{
	double n,i,s=0,t=0,f=1;
	cin>>n;
	for (i=1;i<=n;i++)
	{	
		t=t+f*(2*i-1);
		s=s+1.0/t;
		f=-f;
	}
	printf("%.2lf\n",s);
}

Java :

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double sum =0;
        for (int i = 1; i <= n; i++){
            sum+=getSum(i);
        }
        System.out.printf("%.2f",sum);
    }
    public static double getSum(int n){
        double sum = 0;
        for (int i = 1; i<=n;i++){
            sum+=(2*i-1)*Math.pow(-1,i+1);
        }
        return 1/sum;
    }
}

Python :

# coding=utf-8
#python2
n=int(input())
s=0
for i in range(1,n+1):
    q=0
    for j in range(i):
        x=(j+1)*2-1
        if (j+1)%2==0:
            q-=x
        else:
            q+=x        
    s+=1.0/q
print("%.2f"%s)

C# :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp2
{
    internal class Program
    {
        static void Main()
        {
           
            int sum = 0;
          
            int n = Convert.ToInt32(Console.ReadLine());
            double ans = 0;
            for (int i = 1; i <= n; i++)
            {
                if (i % 2 == 1)
                {
                    sum = sum + 2 * i - 1;
                }
                else
                {
                    sum = sum - 2 * i + 1;
                }
                ans = ans + 1.0 / sum;
            }
            Console.WriteLine(ans.ToString("0.00")); 
            Console.ReadKey();
     
        }
    }
}