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

#define rep(i,n) for(int i = 0; i < (int)n; i++)
#define FOR(n) for(int i = 0; i < (int)n; i++)
#define repi(i,a,b) for(int i = (int)a; i < (int)b; i++)
#define pb push_back
#define m0(x) memset(x,0,sizeof(x))
#define fill(x,y) memset(x,y,sizeof(x))
#define bg begin()
#define ed end()
#define all(x) x.bg,x.ed
#define vi vector<int>
#define vvi vector<vi>
#define vll vector<ll>
#define vvll vector<vll>
#define vs vector<string>
#define vvs vector<vs>
#define vc vector<char>
#define vvc vector<vc>
#define pii pair<int,int>
#define pllll pair<ll,ll>
#define vpii vector<pair<int,int>>
#define vpllll vector<pair<ll,ll>>
#define vpis vector<pair<int,string>>
#define vplls vector<pair<ll, string>>
#define vpsi vector<pair<string, int>>
#define vpsll vector<pair<string, ll>>

#define int ll

using ll = long long;
using ld = long double;
using ull = unsigned long long;

const ll INF = 1e15;

void solve() {
    string s;
    cin >> s;
    map<char, int> mp;
    FOR(s.size()) {
        mp[s[i]]++;
    }
    FOR(26) {
        char now = 'a' + i;
        if(mp[now] > 0) {
            cout << "a";
            while(mp[now]--) {
                cout << now;
            }
            return;
        }
    }
}

signed main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}