#include <iostream>
#include <map>
using namespace std;
 
int main() {
    string str;
    cin >> str;
 
    map<char, int> freq;  // 문자별 등장 횟수 저장
 
    // 문자열의 각 문자 개수 세기
    for (char c : str) {
        freq[c]++;
    }
 
    char maxChar = 'z' + 1;  // 사전순으로 가장 뒤에 있는 문자보다 큰 값으로 초기화
    int maxCount = 0;
 
    // 최빈 문자 찾기
    for (auto &[c, count] : freq) {
        if (count > maxCount || (count == maxCount && c < maxChar)) {
            maxChar = c;
            maxCount = count;
        }
    }
 
    cout << maxChar << endl;
    return 0;
}
 

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