#include <iostream>
#include <conio.h>
#include <math.h>
using namespace std; // 1. Khai bao thu vien
main ()
{
    int i,n,s;
    s=0;
    do
    {
    cout <<"\n Nhap 1 so nguyen duong = ";
    cin>>n;
    if (n<1)
       cout<<"Loi. yeu cau nhap lai mot so nguyen duong \n";
    }
    while (n<1);
   
   if (n%2==1)
           for (i=1; i<=n;i=i+2)
      
               s= s+i;
           
   else
           for (i=2; i<=n;i=i+2)
      
               s= s+i;
    cout << "tong can tim la = "<<s;
    
    getch();
}