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

constexpr int mod = 1000000007;

long long modpow(long long a,long long b) {
    long long ans = 1;
    while(b) {
        if(b & 1) {
            (ans *= a) %= mod;
        }
        (a *= a) %= mod;
        b /= 2;
    }
    return ans;
}

int main() {
    int N;
    string S;
    cin >> N >> S;
    int ans = 0;
    for(int i = N-1; i >= 0; i--) {
        if(S[i] != 'A') {
            ans += modpow(2,i);
            ans %= mod;
            for(int j = 0; j < i; j++) {
                if(S[j] != 'A' && S[j] != S[i]) {
                    S[j] = 'A';
                }
                else if(S[j] == 'A') {
                    if(S[i] == 'C') S[j] = 'B';
                    else S[j] = 'C';
                }
            }
        }   
    }
    cout << ans << endl;
}