#include <iostream>
#include <chrono>
 
using namespace std;
 
const unsigned long long N = 1000000000ULL;
 
unsigned long long s(unsigned long long n)
{
    unsigned long long s = 0;
 
    for (unsigned long long i = 0; i < n; i++)
        s += i;
 
    return s;
}
 
int main()
{
    auto t1 = std::chrono::high_resolution_clock::now();
 
    auto x = s(N);
 
    auto t2 = std::chrono::high_resolution_clock::now();
    auto t = std::chrono::duration_cast<std::chrono::nanoseconds>(t2 - t1).count();
 
    cout << "Result: " << x << " -- time (ms):" << t/0.1e7 << endl;
}

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