#include <stdio.h>

int main() {
    int n;
    int sum =0;
    scanf("%d",&n);
    for(int m =1;m<=n;m++)
    {
        if(m%2==0)
        {
            sum -= m;
        }
        else 
        {
            sum += m;
        }
    }
    printf("%d",sum);
    return 0;
}