import std.algorithm, std.container, std.conv, std.math, std.range, std.typecons, std.stdio, std.string;

auto rdsp(){return readln.splitter;}
void pick(R,T)(ref R r,ref T t){t=r.front.to!T;r.popFront;}
void readV(T...)(ref T t){auto r=rdsp;foreach(ref v;t)pick(r,v);}
void readC(T...)(size_t n,ref T t){foreach(ref v;t)v=new typeof(v)(n);foreach(i;0..n){auto r=rdsp;foreach(ref v;t)pick(r,v[i]);}}

void main()
{
  int n; readV(n);
  string[] s; readC(n, s);

  auto c = new int[][](26, n);
  foreach (i, si; s)
    foreach (ch; si)
      c[ch-'a'][i]++;

  foreach (i; 0..26)
    write((cast(dchar)('a'+i)).repeat.take(c[i].reduce!min));
  writeln;
}
