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

alias sread = () => readln.chomp();
ulong bignum = 1_000_000_007;
alias Pair = Tuple!(long, "number", long, "times");

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;
    }
}

void main()
{
    auto n = lread();
    if(n == 1)
    {
        readln.chomp.writeln();
        return;
    }
    auto strary = new string[](n);
    auto alfary = new long[][](n, 26);
    auto alf_min = new long[](26);
    foreach (ref e; strary)
    {
        e = sread();
        sort(cast(ubyte[]) e);
    }
    foreach (i, e; strary)
    {
        foreach (f; e)
        {
            alfary[i][f - 'a']++;
        }
    }

    foreach (i, e; alfary)
    {
        foreach (j, f; e)
        {
            if (alf_min[j])
                alf_min[j] = min(f, alf_min[j]);
            else if(i != n - 1)
                alf_min[j] = f;
        }
    }

    foreach (i, e; alf_min)
    {
        print_n_times('a' + i, e);
    }
    writeln();
}

void print_n_times(ulong c, long n)
{
    foreach (_; 0 .. n)
    {
        c.to!(char).write();
    }
}
