input()
dp = [0] * 3
w = 0
for c in input():
    p = ord(c) - ord('A')
    dpnxt = [max(dp) * 2 + w * 2 + 100] * 3
    for d in range(3):
        if d == p:
            dpnxt[d] = min(dpnxt[d], dp[d])
        else:
            dpnxt[p] = min(dpnxt[p], dp[d] + w)
            dpnxt[d ^ p ^ 3] = min(dpnxt[d ^ p ^ 3], dp[d] + w + 1)
            dpnxt[d] = min(dpnxt[d], dp[d] + w * 2 + 1)

    dp = dpnxt.copy()
    w = w * 2 + 1

print(dp[0] % 1000000007)