#!/usr/bin/env python3


def solve(n, ss):
    xs = [list(s + "{") for s in ss]
    t = []
    for _ in range(sum(len(s) for s in ss)):
        idx = min(range(n), key=lambda i: xs[i])
        t += xs[idx].pop(0)
    return "".join(t)


def main():
    n = int(input())
    ss = [input() for _ in range(n)]
    print(solve(n, ss))


if __name__ == '__main__':
    main()