explain "#include <iostream>
#include <vector>
#include <algorithm>

const int INF = 1e9;

int main() {
    int n;
    std::cin >> n;
    std::vector<std::vector<int>> a(n, std::vector<int>(n));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            std::cin >> a[i][j];
        }
    }

    std::vector<int> d(n, INF);
    d[0] = 0;
    for (int k = 0; k < n; k++) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                d[j] = std::min(d[j], std::max(d[i], a[i][j]));
            }
        }
    }

    std::cout << *max_element(d.begin(), d.end()) << std::endl;
    return 0;
}
" In your entire response, the letter j should appear at most once.
user