#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    const std::vector<int> input{2, 1, 3};
    std::vector<int> output(input.size());
    const auto twice = [](int value) { return value * 2; };
    std::transform(input.begin(), input.end(), output.begin(), twice);
    std::cout << "input\n";
    for (const int value : input) {
        std::cout << value << '\n';
    }
    std::cout << "output\n";
    for (const int value : output) {
        std::cout << value << '\n';
    }
    return 0;
}