3
rjnflsbpxqivrcdjptj
vpojopbwbwbswdu
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 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
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 5
splt
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 2
hk
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 5
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abcdefghijklmnopqrst
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 2
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 5
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abcdefghijklmnopqrst
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qqq
 1
epkotfpkkrhhmuipmtdk
 10
kpmwcdoysw
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kuzoxmiixxbl
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jhbplhpklrgwnaugdf
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lxyzgcmbzulcst
 5
dfijdfhi
abcdefghijklmnopqrst
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jty
 2
xlaxwpjabtpwddc
txwdjmohrrszorrnomc
 1
a
 30
waiphwcqrrinr
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doxnxbjwptnimjmsuijx
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xpbtbpftimnn
khbknqbvdkdd
mldj
skrvnyz
avptgpjmenfzfxwckmt
 30
e
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itaubd
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x
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ci
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jos
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ge
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t
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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() {
  int n, i, j, x = 0;
  char c[30][30] = {0};
  scanf("%d\n", &n);
  for (i = 1; i <= n; i++) {
    char temp[605] = "";
    cin.getline(temp, 605);
    int length = strlen(temp);
    for (j = 0; j < length; j++) {
      c[0][temp[j] - 96] = 1;
      if (j != length - 1) c[temp[j] - 96][temp[j + 1] - 96] = 1;
    }
  }
  for (i = 0; i <= 26; i++) {
    for (j = 1; j <= 26; j++) {
      if (c[i][j] == 0 && i == 0) {
        printf("%c\n", j + 96);
        x = 1;
      } else if (c[i][j] == 0) {
        printf("%c%c\n", i + 96, j + 96);
        x = 1;
      }
      if (x == 1) return 0;
    }
  }
  return 0;
}
