#include <iostream>
#include <iomanip>
#include <string>
#include <algorithm>
#include <cmath>
using namespace std;
 
 
int main(void)
{
	string sentence;
	getline(cin, sentence);
	int alphabet[26] = { 0 };
	int temp[26] = { 0 };
	for (int i = 0; sentence[i] !='\0'; i++)
	{
		if (sentence[i] != ' ')    //띄어쓰기가 아니라면
		{
			alphabet[sentence[i] - 'a']++;    //그 알파벳의 해당 인덱스에 저장된 숫자를 1씩 증가 (a는 0번째 인덱스)
			temp[sentence[i] - 'a']++;
		}
	}
	sort(alphabet, alphabet + 26);    //최다 쓰인 횟수가 몇번인지 알기 위해 조사
	for(int k = 0; k < 26; k++)
	{
		if (temp[k] == alphabet[25])  //최다인 25번째 인덱스안에 저장된 숫자만큼 쓰였으면 출력
			cout << char(k + 'a');    //아스키코드를 이용해서 인덱스에 숫자  97을 더한 문자 출력
	}
	return 0;
}

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YgpiCmEKYQpj

b
b
a
a
c