#include <bits/stdc++.h>
using namespace std;
using namespace chrono;
using ld = long double;
using ll = long long;
template<class time_unit>
class timer: high_resolution_clock {
const time_point start_time;
public:
timer(): start_time(now()) {}
rep elapsed_time() const {
return duration_cast<time_unit>(now()-start_time).count(); } };
inline void average_time(ld u) {
cout << "average time per iteration = " << fixed << setprecision(10),
cout << u << " nsec."; }
inline ll arithmetic_series_sum(int n) {
timer<nanoseconds> t; ll sum = 0;
for (int i = n; i > 0; --i)
sum += i;
average_time(ld(t.elapsed_time())/n);
return sum; }
int main() {
int n; cin >> n, assert(arithmetic_series_sum(n) == 1ll*(n+1)*n/2); }
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