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

typedef int T;

int main() {
    std::vector<std::vector<T>> vec = {
        {2, 8, 1, 4},
        {3, 7, 6, 7},
        {3, 3, 4, 9},
        {8, 6, 3, 4},
        {7, 1, 5, 7}
    };
    int idx = 2;
    std::sort(vec.begin(), vec.end(), [idx](const std::vector<T>& a, const std::vector<T>& b) {
        return a.at(idx) < b.at(idx);
    });
    for (size_t i = 0; i < vec.size(); i++) {
        for (size_t j = 0; j < vec[i].size(); j++) {
            std::cout << vec[i][j] << (j + 1 < vec[i].size() ? ' ' : '\n');
        }
    }
    return 0;
}