#include <iostream>
#define N 1001
using namespace std;
struct mutare
{
    char x, y;
} mutari[N];
int nA, A[N], nB, B[N], nC, C[N];
int nrm,n;

int main()
{
    cin>>nA;
    for(int i=1; i<=nA; i++) cin>>A[i];
    n=nA;
    for(int i=1; i<=n; i++)
        if(B[nB]==i) ///B pe C
        {
            C[++nC]=i;
            nB--;
            nrm++;
            mutari[nrm].x='B';
            mutari[nrm].y='C';
        }
        else
        {
            bool gasit=0;
            while(nA>0 &&!gasit)
                if(A[nA]==i) /// A pe C
                {
                    C[++nC]=i;
                    nA--;
                    nrm++;
                    mutari[nrm].x='A';
                    mutari[nrm].y='C';
                    gasit=1;
                }
                else /// A pe B
                {
                    B[++nB]=A[nA];
                    nA--;
                    nrm++;
                    mutari[nrm].x='A';
                    mutari[nrm].y='B';
                }
            if(gasit==0){cout<<0; return 0;}
        }
       cout<<nrm<<'\n' ;
       for(int i=1;i<=nrm;i++)
        cout<<mutari[i].x<<' '<<mutari[i].y<<'\n';
    return 0;
}