#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int N;
string S,T;
const ll mo=1000000007;
ll dp[1010];
void solve() {
	int i,j,k,l,r,x,y; string s;
	
	dp[0]=0;
	for(i=1;i<=1000;i++) dp[i]=(dp[i-1]*2+1)%mo;
	
	cin>>N>>S;
	T=string(N,'A');
	ll ret=0;
	for(i=N-1;i>=0;i--) {
		if(S[i]!=T[i]) {
			int a=(int)'A'+'B'+'C'-S[i]-T[i];
			FOR(j,i) T[j]=a;
			ret+=dp[i]+1;
		}
	}
	cout<<ret%mo<<endl;
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}