import std.conv, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) throw new EOFException; tokens = readln.split; } auto token = tokens[0]; tokens.popFront; return token; }
int readInt() { return readToken().to!int; }
long readLong() { return readToken().to!long; }
real readReal() { return readToken().to!real; }

void chmin(T)(ref T t, in T f) { if (t > f) t = f; }
void chmax(T)(ref T t, in T f) { if (t < f) t = f; }

int binarySearch(T)(in T[] as, in bool delegate(T) test) { int low = -1, upp = cast(int)(as.length); for (; low + 1 < upp; ) { int mid = (low + upp) >> 1; (test(as[mid]) ? low : upp) = mid; } return upp; }
int lowerBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a < val)); }
int upperBound(T)(in T[] as, in T val) { return as.binarySearch((T a) => (a <= val)); }


int N;
string[] S;

void main() {
  try {
    for (; ; ) {
      N = readInt();
      S = new string[N];
      foreach (i; 0 .. N) {
        S[i] = readToken();
      }
      
      string ans;
      auto s = S.dup;
      foreach (i; 0 .. N) {
        s[i] ~= '~';
      }
      for (; ; ) {
        s.sort;
        if (s[0][0] == '~') {
          break;
        }
        ans ~= s[0][0];
        s[0] = s[0][1 .. $];
        if (s[0].empty) {
          s = s[1 .. $];
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}