import core.bitop;
import std.algorithm;
import std.ascii;
import std.bigint;
import std.conv;
import std.functional;
import std.format;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.random;
import std.typecons;

alias sread = () => readln.chomp();
alias Point2 = Tuple!(long, "y", long, "x");

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}

enum MOD = (10 ^^ 9) + 7;

void main()
{
    long N = lread();
    long[long] D;
    foreach (c; sread())
        D[c] = (c in D) ? D[c] + 1 : 1;
    foreach (_; 1 .. N)
    {
        string S = sread();
        long[long] d;
        foreach (c; S)
            d[c] = (c in d) ? d[c] + 1 : 1;
        foreach (key, val; D)
            D[key] = (key in d) ? min(d[key], val) : 0;

    }
    auto keys = D.keys;
    auto vals = D.values;
    zip(keys, vals).sort();
    string ans;
    foreach (i; 0 .. keys.length)
        ans ~= repeat(cast(char) keys[i]).take(vals[i]).array;
    writeln(ans);
}
