function main(input) {
    const numbers = input.split("\n")[0].split(" ").map( v => Number(v));
    const list = JSON.parse(JSON.stringify(input.split("\n")));
    list.shift();
    const listSorted = list.sort();

    console.log(listSorted.join(''));
}


// let input = "3 3" + '\n' +
// "dxx" + '\n' +
// "axx" + '\n' +
// "cxx"

// main(input);
main(require("fs").readFileSync("/dev/stdin","utf8"));
  