#include<stdio.h>
void calculatesumofsquares(int n){
int sum = 0;
int sign = (n<0)?-1:1;
int limit = abs(n);
for(int i = 1; i<=limit;i++){
    if(i%2==0){
        sum +=(i*i);
    }else{
        sum -=(i*i);
    }
}
printf("%d\n",sum*sign);
}
int main(){
int n;
if(scanf("%d",&n)==1){
calculatesumofsquares(n);
}
return 0;
}