#include<stdio.h>
#include<math.h>
int main()
{
 int count = 2;
 int sum = 0;
 int tal;

 printf("Skriv in tal: ");
 scanf("%d", &tal);

 while (count <= tal)
 {
  sum+=count;
  count++;
  count++;


 }
 printf("%d", sum);

 getchar();
 getc(stdin);
 return 0;
}