#include <iostream>
#include <string>
using namespace std;
char alphabet[26] = { 'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z' };
int check[26];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
string s;
while (cin >> s) {
for (int i = 0; i < s.length(); i++) { //์ํ๋ฒณ ๊ฐฏ์ ํ์
for (int k = 0; k < 26; k++) {
if (s[i] == alphabet[k]) check[k]++;
}
}
}
int maxIndex = 0;
for (int i = 0; i < 26; i++) { //์ํ๋ฒณ ๊ฐฏ์๊ฐ ์ ค ๋ง์๊ฒ ๋ช๊ฐ์ธ์ง ํ์
if (check[i] > maxIndex) {
maxIndex = check[i];
}
}
for (int i = 0; i < 26; i++) {
if (check[i] == maxIndex) cout << alphabet[i]; //์ต๋ ๊ฐฏ์๊ฐ ์ค๋ณต์ผ์๊ฐ ์์ผ๋ ์ ๋ถ์ถ๋ ฅ
}
}
๋๊ธ