easy

#include<iostream>
#include<string>
#include<cstring>
using namespace std;
int cha[256] = {};
const int _Inf = -0x7fffffff;
char find_max_char(int m)
{
    char c = ' ';
    for(int i = 97;i <= 122;i++){if(cha[i] == m){c = char(i);break;}}
    return c;
}
char take_max()
{
    char c = ' ';
    int maxn = _Inf;
    for(int i = 97;i <= 122;i++){if(cha[i] > maxn)maxn = cha[i];}
    c = find_max_char(maxn);
    return c;
}
int main()
{
    string s;
    cin >> s;
    for(int i = 0;i < s.size();i++){cha[int(s[i])]++;}
    cout << take_max();
    return 0;
}