#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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