C :

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
int main()
{
   // freopen("in","r",stdin);
 //   freopen("out","w",stdout);



	int  n;
	while(scanf("%d",&n )!=EOF){


	int i, sum = 0;

	for (i = 1; i <=n; i = i+2)
	{
		sum = sum + i;
	}

	printf("%d\n", sum);

	}
  return 0;
}

C++ :

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

	return 0;
}