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()
{
    long n = lread();
    auto all_have = new long['z' - 'a' + 1];
    foreach (i; 0 .. n)
    {
        auto s = sread();
        auto now = new long['z' - 'a' + 1];
        foreach (e; s)
        {
            if (!i)
                all_have[e - 'a']++;

            now[e - 'a']++;
        }
        foreach (e; 'a' .. 'z' + 1)
        {
            all_have[e - 'a'] = min(now[e - 'a'], all_have[e - 'a']);
        }
    }
    foreach (i, e; all_have)
    {
        if(e)
        {
            long j;
            while(j++ < e)
                write(cast(char)('a' + i));
            
        }
    }
    writeln();
}
