#include <bits/stdc++.h>
using namespace std;

int main(){
	string s;
	int i,x;
	getline(cin,s);
	int a[200] = {0};
	for(i = 0;i < s.size();i++){
		x = s[i];
		a[x]++;
	}
	
	char c;
	int max = 0;
	for(i = 'z';i >= 'a';i--){
		if(a[i] > max){
			max = a[i];
			c = i;
		}
	}
	cout<<c<<endl;
}