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() {
  map<string, int> a;
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    string q;
    cin >> q;
    for (int l = 0; l <= q.size() - 1; l++) {
      char p[50];
      for (int i = 0; i <= 49; i++) p[i] = 0;
      int o = 0;
      for (int j = l; j < q.size(); j++) {
        p[o++] = q[j];
        a[p] = 1;
      }
    }
  }
  char p[50];
  for (int i = 0; i <= 49; i++) p[i] = 0;
  int o = 0;
  int s = 0;
  while (1) {
    if (!s) {
      p[o] = 'a';
      if (!a.count(p)) {
        cout << p;
        return 0;
      }
      s = 1;
      continue;
    }
    p[o]++;
    int s = o;
    while (p[o] > 'z') {
      p[o] = 'a';
      o--;
      if (o < 0) {
        p[s + 1] = 'a';
        s++;
        break;
      } else if (o >= 0) {
        p[o]++;
      }
    }
    o = s;
    if (!a.count(p)) {
      cout << p;
      return 0;
    }
  }
}
