#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N=25;
int n;
vector<pair<char,char>>v;
char pos[N];
int sum='A'+'B'+'C';
void solve(int n,char from,char to,char g){
    if(n==0)return ;
    if(from==to){
        solve(n-1,pos[n-1],to,sum-pos[n-1]-to);
        return ;
    }
    solve(n-1,pos[n-1],g,sum-pos[n-1]-g);
    v.push_back({from,to});
    for(int i=1;i<=n-1;i++)pos[i]=g;
    solve(n-1,g,to,from);
}
main()
{
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>pos[i];
    }
    while(n>0&&pos[n]=='C')n--;
    if(n==0)return cout<<0,0;
    solve(n,pos[n],'C',sum-'C'-pos[n]);
    cout<<v.size()<<'\n';
    for(auto x:v)cout<<x.first<<x.second<<'\n';
    return 0;
}