#include<stdio.h>
main()
{
int a;
int b=1;
long c=0;

printf("1000ikanosuujiwonyuuryousitekudasai:");
scanf("%d",&a);
while(a<1001)
{
while(b<=a)
{
c=c+b;
b=b+2;
}
a=1001;
}
printf("%ld",c);
}