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

bool cmp(pair<int,string>p1, pair<int,string>p2)
{
    return p1.first < p2.first;
}

bool cmp2(string p1, string p2)
{
    int tam = min(p1.length(), p2.length());
    
    for(int i=0;i<tam;i++)
    {
        char c1 = tolower(p1[i]), c2 = tolower(p2[i]);
        if( c1<c2)
            return true;
        if(c2<c1)
            return false;
    }
    return p1.length() < p2.length();

    
}


int main() {
    // your code goes here
    int n, tmp;
    cin>>n;
    
    string cad;
    map<string,int> V1;
    vector<string> names;

    int all =0;
    
    for(int i=0;i<n;i++)
    {
        cin>>cad;
        V1[cad]++;
        all++;
    }

    if(V1[cad]==n)
    {
        cout<<"0"<<endl;
        return 0;
    }
  
    bool band = true;

    map<string, int>:: iterator it;
    vector< pair<int, string > >resi;

    int additional = 0;
        
    band =false;
    int lowest = 1000000;
    for (it=V1.begin(); it!=V1.end(); ++it)
    {
        int p_c = (it->second);
        lowest = min(lowest, p_c);
    }
           
    for (it=V1.begin(); it!=V1.end(); ++it)
    {
        int p_c = (it->second);
        if(p_c == lowest)
        {
            names.push_back(it->first);
            additional+= it->second;
        }
        else
        {
            resi.push_back(pair<int,string>(it->second, it->first));
        }
    }

    
    if(int(resi.size()) !=0)
    {

        vector<int>cum;
        tmp = 0;

        sort(resi.begin(), resi.end(), cmp);
        for(int i=0;i<int(resi.size());i++)
        {
            cum.push_back(tmp+resi[i].first);
            tmp = cum[i];
        }

        int ind = 0;
        for(int i=0;i<int(resi.size())-1;i++)
        {
            //cout<<cum[i]+additional<<" "<<resi[i+1].first<<endl;            
            if(cum[i]+additional<resi[i+1].first)
                ind = i+1;
        } 
        for(int i=0;i<ind;i++)
            names.push_back(resi[i].second);

        //cout<<ind<<endl;

        if(ind == 0)
        {
            for(int i=0;i<int(resi.size())-1;i++)
            {
                if(cum[i]+additional==resi[i+1].first)
                    ind = i+1;
            }
            for(int i=0;i<ind;i++)
                names.push_back(resi[i].second);
        }
    }

//    vector<string> names_l;
//    map<string, string> NA;
//    int tam = names.size();
//
//    for(int i=0; i<tam;i++)
//    {
//        string s2 = names[i];
//        transform(s2.begin(), s2.end(), s2.begin(), ::tolower);
//        names_l.push_back(s2);
//        NA[s2] = names[i];
//    }
//   
//
//    sort(names_l.begin(), names_l.end());
//    cout<<tam<<endl;
//    for(int i=0;i<tam;i++)
//        cout<<NA[names_l[i]]<<endl;
//
//

    int tam = names.size();
    sort(names.begin(), names.end());
    cout<<tam<<endl;
    for(int i=0;i<tam;i++)
        cout<<names[i]<<endl;
    return 0;
}