#include<bits/stdc++.h> using namespace std; //int a; int n,a,b,sum=0; int main(){ /**cin>>a; int jsum=0; int osum=0; for(int i=1;i<=a;i++){ if(i%2==0) osum+=i; else jsum+=i; } cout<<jsum<<" "<<osum;**/ cin>>n; for(int i=2;i<=n;i++){ if(i%2==0) sum+=i; else sum-=i; } cout<<sum+1; return 0; }