#include<iostream> #include<cstdio> //scanf()\printf() #include<cstring> #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int n,s=1; cin>>n; for(int i=2;i<=n;i++){ if(i%2==0) s+=i; else s-=i; } cout<<s; return 0; }