include<stdio.h>

int main(){
int n;
scanf("%d",&n);
if(n % 2 == 0){ //遇到一次偶数则执行加一次-1
printf("%d",(n/2)*(-1));
}else{ //遇到一次奇数求从1到n等差数列和
printf("%d",(n+1)/2);
}
return 0;
}