C :

#include<stdio.h>

void main(){
    double s=0;
    int i,n,f=1;
    scanf("%d",&n);

    for(i=1;i<=n;i++){
        s=s+1.0*f/i;
        f=f*-1;
    }  
    printf("%.4f",s);
}

C++ :

#include <bits/stdc++.h>
using namespace std;
int main(){
    float s = 0;
	int i,f = 1,n;
	cin>>n;
	for(i = 1;i <= n;i++){
		s = s + 1.0 * f / i;
		f = f * -1;
	} 
    cout<<fixed<<setprecision(4)<<s<<endl;
} 

Java :

import java.util.*;
public class Main{
	public static void main(String args[]){
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();
		double a = 1.0;
		double sum = 0;
		for(int i = 1;i<=n;i++){
			if(i%2==0){
				 sum =sum-(a/i);
			}else{
				sum =sum+(a/i);
			}
		}
		System.out.println(String.format("%.4f",sum));
	}
}

Python :

n=int(input())
i=1
j=2
a=0
b=0
while i<=n:
    a+=1/i
    i+=1
while j<=n:
    b+=1/j
    j+=2
print('{:.4f}'.format(a-2*b))