def str_to_modint(S: str, A: int, M: int) -> int:
    res = 0
    for a in S:
        res = (A * res + int(a)) % M
    return res

def solve():
    Mod = pow(10, 9) + 7
    A = int(input())
    B_str = input()

    B_mod = str_to_modint(B_str, A, Mod)
    d = len(B_str) - 1

    ans = 0
    for i in range(1, d + 1):
        ans += (pow(A, i, Mod) - pow(A, i - 1, Mod)) * (i - 1) % Mod

    ans += (B_mod - pow(A, d, Mod) + 1) * d

    return ans % Mod

#==================================================
print(solve())