#include<stdio.h>
main()
{int n,i,sign=1,sum=0;
scanf("%d",&n);
for(i=1;i<=n;i++)
{sum=sum+sign*i;
sign*=-1;}
printf("%d",sum);}
main()
{int n,i,sign=1,sum=0;
scanf("%d",&n);
for(i=1;i<=n;i++)
{sum=sum+sign*i;
sign*=-1;}
printf("%d",sum);}