#include <iostream>
#include <string>
using namespace std;
int main()
{
int i, m,min;
int a[26];
string str,temp;
while (cin >> str)
{
for (int i = 0; i < 26; i++)
a = 0; //初始化数组都为0
m = str.size();
for (i = 0; i<m; i++)
a[str-'a']++; //计数
min = a[str[0]-'a'];
for (i = 0; i<m; i++)
if (a[str - 'a'] <= min)
min = a[str-'a'];
for (i = 0; i < m; i++)
if (a[str - 'a'] > min)
cout << str;
cout << endl;
}
return 0;
}