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