#include <iostream>
#include <iomanip>
#include <cstdio>
#include <stdio.h>
#include <cstdlib>
#include <bitset>
#include <memory>
#include <algorithm>
#include <set>
#include <map>
#include <vector>
#include <list>
#include <string>
#include <cstring>
#include <fstream>
#include <functional>
#include <stack>
#include <complex>
#include <wchar.h>
#include <wctype.h>
#include <cmath>
#include <queue>
#include <ctime>
#include <numeric>
#include <bitset>
#include <cassert>


using namespace std;

template<typename T> T mabs(const T &a){ return a<0?-a:a;}
#define rep(x,y,z) for(int x=(y),e##x=(z);x<e##x;x++)
#define SQR(x) ((x)*(x))
#define all(c) (c).begin(), (c).end()

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef unsigned int ui;
typedef short int si;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef pair<double, int> pdi;
typedef pair<double, double> pdd;



void run()
{
    int n;
    cin>>n;
    char str[100];
    scanf("%s",str);
    reverse(str, str+strlen(str));
    char pos = 'A';
    ll res = 0;
    rep(i,0,n)
    {
        if (str[i] != pos)
        {
            pos = 'A' + 'B' + 'C' - str[i] - pos;
            res += (1LL<<(n-i-1));
        }
    }
    cout<<res<<endl;
}




int main()
{
#ifdef _MONYURA_
#ifdef prob
    freopen(prob".in","r",stdin);
    freopen(prob".out","w",stdout);
#else
    freopen("test.in","r",stdin);
    freopen("test.out","w",stdout);
#endif
    time_t st=clock();
#else
#ifdef prob
    freopen(prob".in","r",stdin);
    freopen(prob".out","w",stdout);
#endif
#endif
    run();
#ifdef _MONYURA_
#ifndef prob
    printf( "\n=============\n");
    printf("Time: %.2lf sec\n",(clock()-st)/double(CLOCKS_PER_SEC));
#endif
#endif

    return 0;
}