C++ :

#include<iostream>
#include<iomanip>
#include<cstdio>
#include<cmath>
using namespace std;
long long s,n;
int main()
{
  cin>>n;
  for(int i=1;i<=n;i++)
     if(i%2!=0)  s+=i;
     cout<<s<<endl;
 
 
   return 0;
 
}

Java :

import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner in=new Scanner(System.in);
        while(in.hasNext()){
        int N=in.nextInt();
        int sum=0;
        for(int i=1;i<=N;i++){
            if(i%2!=0){
                sum+=i;
            }
        }
        System.out.println(sum);
    }
}
}