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