#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
string a[100005], f[100005], ans[100005];
int cur, cnt;
int main() {
	char c;
    while(cin>>c){
        if(isupper(c))
            a[++cnt] = c;
        else a[cnt] += c;
    }
	for(int i = 1; i <= cnt; i++){
		if(a[i] > f[cur])
			f[++cur] = a[i];
		else {
            int p = lower_bound(f+1,f+cur+1,a[i]) - f;
			f[p] = a[i];
            ans[p] = ans[p-1]+a[i];
		}
	}
	cout << ans[cur] << endl;
    return 0;
}