include<iostream>
#include<string>
#include<vector>
using namespace std;
int main()
{  string str;  cin >> str;  int len = str.size();  vector<int> dp(len, 1);  vector<char> ans;  int maxlen = 1;  int k = 0;  for (int i = 1; i < len; i++)  {  if (str[i] == str[i - 1])  dp[i] = dp[i - 1] + 1;  if (dp[i] > maxlen)  maxlen = dp[i];  }  for (int i = 0; i < len; i++)  {  if (dp[i] == maxlen)  {  ans.push_back(str[i]);  }  }  if (ans.size() > 1)  {  cout << ans[k];  for (k = 1; k < ans.size(); k++)  {  cout << ';' << ans[k];  }  cout << endl;  }  else  {  cout << ans[k] << endl;  }  return 0;
}