#include <iostream>
using namespace std;
long long sum_even, sum_odd, n;
int main() {
sum_even = 0;
sum_odd = 0;
cin >> n;
for (int i = 1 ; i <= n ; i++) {
if (i % 2 == 0) {
sum_even += i;
} else {
sum_odd += i;
}
}
cout << sum_odd - sum_even << endl;
return 0;
}

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