#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int sum(int n){
double s=0;
for(int i=1;i<=n;i++){
s+= (pow(-1,i+1))*i;
}
return s;
}
int main(){
int n;
cin>>n;
int s=sum(n);
cout<<s;
return 0;
}
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