#include<iostream>
using namespace std; 
int main()
{ 
    int a,x=0;
    cin>>a;
    for(int i=1;i<=a;i=i+2)
	{
        x+=i;	
	}
	cout<<x<<endl;
    return 0;
}

C :

#include <stdio.h>

int main(){
    int i,n,s = 0;
    scanf("%d",&n);
    for(i = 1;i <= n;i = i + 2){
       s = s + i;
    }
    printf("%d\n",s);
    
    return 0;
}

C++ :

#include <bits/stdc++.h>

using namespace std;

int main(){
    int n;
    cin>>n;
    int i,c=0;
    for(i=1;i<=n;i=i+2){
        c=c+i;	
	}cout<<c<<endl;
    return 0;
}

Python :

n =  int(input());
s = 0;
for i in range(1,n + 1):
    if i % 2 == 1:
      s = s + i;
print(s);