C :

#include<stdio.h> 
int main()
{
    int i,n,s=0;
    scanf("%d",&n); 
    for(i=1; i<=n ;i+=2)
    {
     s=s+i;
    }
    printf("%d",s);
    return 0;
}

C++ :

#include <iostream>

using namespace std;

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

Python :

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