MOD = 10 ** 9 + 7

n = int(input())
C = [0]
for _ in range(n):
    C.append(C[-1] * 2 + 1)

S = input().rstrip("A")
if not S:
    print(0)
    exit()

if len(S) == 1:
    print(1)
    exit()

dp = [1] * 3
s = "ABC".index(S[0])
dp[s] = 0

for x, s in enumerate(S[1:], 1):
    s = "ABC".index(s)
    ndp = [float("inf")] * 3
    for i in range(3):
        for j in range(3):
            if j == s:
                if i == j:
                    ndp[i] = min(ndp[i], dp[j])
                else:
                    ndp[i] = min(ndp[i], dp[j] + C[x + 1])
            else:
                if i == j:
                    ndp[i] = min(ndp[i], dp[j] + 2 * C[x] + 1)
                elif i == s:
                    ndp[i] = min(ndp[i], dp[j] + C[x])
                else:
                    ndp[i] = min(ndp[i], dp[j] + C[x] + 1)
    dp = ndp
print(dp[0] % MOD)