MOD = 10 ** 9 + 7
a = int(input())
b = input()
x = 0
for c in b:
    x *= a
    x += ord(c) - ord('0')
    x %= MOD
ans = (x - (pow(a, len(b) - 1, MOD) - 1)) * (len(b) - 1)
for i in range(len(b) - 1):
    ans += i * pow(a, i, MOD) * (a - 1)
print(ans % MOD)