#include <bits/stdc++.h>
using namespace std;
int main(){
    string s1;
    int x;
    getline(cin,s1);
    int a[200]={0};
    for(int i=0;i<s1.size();i++){
        x=s1[i];
        a[x]++;
    }
    char c;
    int max=0;
    for(int i='z';i>='a';i--){
        if(a[i]>max){
            max=a[i];
            c=i;
        }
    }
    cout<<c;
}
/**************************************************************
	Problem: 1478
	User: xuanhua
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2076 kb
****************************************************************/