a = int(input())
S = list(map(int, list(input())))
n = len(S)
mod = 10**9 + 7

ans = 0
cnt = 1
for i in range(n):
    cnt += pow(a, i, mod) * S[n - i - 1]
    cnt %= mod
    if i < n - 1:
        ans += i * (pow(a, i + 1, mod) - pow(a, i, mod)) % mod
    else:
        ans += i * (cnt - pow(a, i, mod) + mod) % mod
    ans %= mod
print(ans)