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
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o
a
u
 5
splt
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knojbur
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 2
hk
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 5
zzxpfk
abcdefghijklmnopqrst
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srgkjaskldfkln
vgnsdfdgfh
 2
rxscdzkkezud
wjehahqgouqvjienq
 5
ojdfhi
abcdefghijklmnopqrst
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ddfhdfhlasjt
qqq
 1
epkotfpkkrhhmuipmtdk
 10
kpmwcdoysw
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kuzoxmiixxbl
crgqtuo
jhbplhpklrgwnaugdf
zuxdaat
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qwghrkqwkobrgevsjrk
tdxgc
lxyzgcmbzulcst
 5
dfijdfhi
abcdefghijklmnopqrst
uvwxy
kopsdfgiopjipw
jty
 2
xlaxwpjabtpwddc
txwdjmohrrszorrnomc
 1
a
 30
waiphwcqrrinr
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qiqehzmgsjdoqd
kjexeesevrlowxhghq
judikhzkj
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jrsrvsvbaiumlmkptn
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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
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q
cvdu
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jos
qy
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nayke
ge
s
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qwad
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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;
char s[30][25];
char a[30];
int n;
int flag = 0;
void dfs(int l, int goal) {
  int i, j;
  if (l == goal) {
    a[l] = 0;
    for (j = 0; j < n; ++j) {
      if (strstr(s[j], a)) break;
    }
    if (j == n) {
      puts(a);
      flag = 1;
    }
    return;
  }
  for (i = 0; i <= 25; ++i) {
    a[l] = i + 'a';
    dfs(l + 1, goal);
    if (flag) return;
  }
}
int main() {
  int i;
  scanf("%d", &n);
  for (i = 0; i < n; ++i) {
    scanf("%s", s[i]);
  }
  for (i = 1; i < n; ++i) {
    dfs(0, i);
    if (flag) break;
  }
  return 0;
}
