3
rjnflsbpxqivrcdjptj
vpojopbwbwbswdu
rydkiwnugwddcgcrng
 1
z
 30
b
u
p
n
f
m
t
i
j
k
p
h
a
c
w
z
z
p
t
d
o
w
u
q
l
y
i
o
a
u
 5
splt
ohqykk
xqpz
knojbur
pmfm
 2
hk
obsp
 5
zzxpfk
abcdefghijklmnopqrst
uvwxz
srgkjaskldfkln
vgnsdfdgfh
 2
rxscdzkkezud
wjehahqgouqvjienq
 5
ojdfhi
abcdefghijklmnopqrst
uvwxyz
ddfhdfhlasjt
qqq
 1
epkotfpkkrhhmuipmtdk
 10
kpmwcdoysw
gtpr
kuzoxmiixxbl
crgqtuo
jhbplhpklrgwnaugdf
zuxdaat
aycv
qwghrkqwkobrgevsjrk
tdxgc
lxyzgcmbzulcst
 5
dfijdfhi
abcdefghijklmnopqrst
uvwxy
kopsdfgiopjipw
jty
 2
xlaxwpjabtpwddc
txwdjmohrrszorrnomc
 1
a
 30
waiphwcqrrinr
o
qiqehzmgsjdoqd
kjexeesevrlowxhghq
judikhzkj
z
xo
lsdzypkfqro
sshgcxsky
gecntpcmoojfwp
svmytmcfhc
jrsrvsvbaiumlmkptn
s
wpcsovfjlyspviflk
ktvyzvddgllht
szahigtmklglrcocbo
znligfxkgxzkcfeu
liryvzmqwhr
xgrxkgiehxztv
etrjxdczppafly
jrdgajschhwsci
doxnxbjwptnimjmsuijx
zciwkbvrhgsjhrr
ehh
bzlnmd
xpbtbpftimnn
khbknqbvdkdd
mldj
skrvnyz
avptgpjmenfzfxwckmt
 30
e
x
itaubd
xcn
v
x
i
ci
aqs
zbi
q
cvdu
a
jos
qy
fjf
nayke
ge
s
q
qwad
gvz
o
ubn
nzoc
h
wnjwjrf
t
bq
bw
 1
b

a
 a
 e
 a
 a
 y
 b
 aa
 a
 ab
 z
 e
 b
 aa
 l
 a

#include <bits/stdc++.h>
using namespace std;
int main() {
  string title[35];
  int d[26];
  int i, j, mx, mn, n, l, cnt;
  char c, t;
  scanf("%d%*c", &n);
  for (i = 0; i < n; i++) cin >> title[i];
  for (c = 'a'; c <= 'z'; c++) {
    mx = 0;
    for (i = 0; i < n; i++) {
      l = title[i].size();
      j = 0;
      cnt = 0;
      while (j < l) {
        if (title[i][j] == c) {
          cnt = 1;
          j++;
          t = c + 1;
          while (j < l) {
            if (title[i][j] != t)
              break;
            else {
              t++;
              j++;
              cnt++;
            }
          }
        } else
          j++;
      }
      if (cnt > mx) mx = cnt;
    }
    d[c - 'a'] = mx;
  }
  mn = 50;
  for (i = 0; i < 26; i++) {
    if (d[i] < mn) {
      mn = d[i];
      j = i;
    }
  }
  for (i = 0; i <= mn; i++) printf("%c", j + i + 'a');
  return 0;
}
