#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
 
string findLDS(const string& sequence) {
    int n = sequence.size();
 
    // dp[i] 表示以 sequence[i] 结尾的最大递减子序列的长度
    vector<int> dp(n, 1);
 
    // 记录最大递减子序列的末尾位置
    vector<int> endPos(n, -1);
 
    for (int i = 1; i < n; ++i) {
        for (int j = 0; j < i; ++j) {
            if (sequence[j] > sequence[i] && dp[j] + 1 > dp[i]) {
            	//sequence[j] > sequence[i] 兩個輸入數列前後數字比較
            	//dp[j] + 1 > dp[i] 是要找j 位置結尾的遞減數列加上當前位置的元素後
            	//是否得到比當前以 i 位置結尾的數列長度更長
                dp[i] = dp[j] + 1;
                endPos[i] = j;
                //dp[i] 表示以 sequence[i] 結尾的最大遞減子序列的長度
                //endPos[i] 則用於記錄這個數列的前一個元素的位置
            }
        }
    }
 
    // 找到最大递减子序列的末尾位置
    int maxLen = 0, maxEndPos = 0;
    for (int i = 0; i < n; ++i) {
        if (dp[i] > maxLen) {
            maxLen = dp[i];
            maxEndPos = i;
        }
    }
 
    // 构造最大递减子序列
    string result;
    while (maxEndPos != -1) {
        result += sequence[maxEndPos];
        maxEndPos = endPos[maxEndPos];
    }
 
    reverse(result.begin(), result.end());
    return result;
}
 
int main() {
    string sequence;
    bool outend = false;
    while (cin >> sequence) {
        string LDS = findLDS(sequence);
        if(!outend){
            cout << LDS;
            outend = true;
        }else{
            cout << endl << LDS;
        }
    }
    return 0;
}
 

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