#include<bits/stdc++.h> using namespace std; int main () { int a,b,i=0,sum=0; cin>>b; for(a=2;a<=b;a+=1){//234 56 789 10 12 if(a%2==0){ i=i+a; }else{ sum=sum+a;//0 } } cout<<i-sum+1; return 0; }