#include<iostream>
#include<algorithm>
#include<vector>
#include<cstdio>
using namespace std;
int main(){
     freopen ("password.in", "r", stdin); freopen
("password.out", "w" , stdout);

    vector<string> otg;
int a;
cin>>a;
string str;
cin>>str;
str+='@';
int last =0;
int maxx=-1;
for(int i=1; i<str.size();i++)
{
    if(str[i]!=str[i-1])
        {
            maxx=max(maxx, i-last);
            otg.push_back(str.substr(last,i-last));
            last = i;
            //cout<<"sfsd "<<i-last<<endl;

        }
}
sort(otg.begin(), otg.end());
int r=0;
//cout<<maxx<<endl;
for(int i=0;i<otg.size();i++)
{
    if(otg[i].size()==maxx) r++;
}
cout<<r<<endl;
for(int i=0;i<otg.size();i++)
{
    if(otg[i].size()==maxx)
        cout<<otg[i]<<endl;
}


return 0;
}