4

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