#include <iostream>
#include <numeric>
#include <vector>
int main() {
    std::vector<int> values{2, 3};
    int copied_total = 0;
    for (auto x : values) { x *= 2; copied_total += x; }
    const auto before = std::accumulate(values.begin(), values.end(), 0);
    for (auto& x : values) x *= 2;
    const auto after = std::accumulate(values.begin(), values.end(), 0);
    if (copied_total != 10 || before != 5 || after != 10) return 1;
    std::cout << "before=" << before << " after=" << after << '\n';
}