ABC_42 - B - 文字列大好きいろはちゃんイージー / Iroha Loves Strings

#include <bits/stdc++.h>

#define forn(l, r) for(int i = l; i < (r); ++i)
#define forj(l, r) for(int j = l; j < (r); ++j)
#define TAM 1000100
#define SYNC ios::sync_with_stdio(0);
#define $ << ' ' <<
#define F first
#define S second
#define endl '\n'


using namespace std;

using ll = long long int;
using ii = pair<int, int>;
using vii = vector<ii>;
using vi = vector<int>;
using graph = vector<vi>;
const int INF = 0x3f3f3f3f;
const int MAXN = 112345;
const ll mod = 1000000007;



int main()
{
    SYNC
    vector<string> vec;
    string s;
    int n, l;
    cin >> n >> l;
    while (n--) {
        cin >> s;
        vec.push_back(s);
    }
    sort(vec.begin(), vec.end());
    for (int i = 0; i < (int) vec.size(); ++i) {
        cout << vec[i];
    }
    cout << endl;


    return 0;
}