# include<iostream> # include<cmath> //# include<bits/stdc++.h>//万能头文件 using namespace std; int main(){ int s=0,n; cin>>n; for(int i=1;i<=n;i++){ if(i==1) s+=i; else if(i%2==0) s+=i; else s-=i; } cout<<s<<endl; return 0; }