MOD = 10 ** 9 + 7

a = int(input())
B = input()
l = len(B)
if l == 1:
    print(0)
    exit()
ans = 0
times = a - 1
for i in range(l - 1):
    ans += i * times
    ans %= MOD
    times *= a
    times %= MOD

tot = 0
times = 1
for b in B[::-1]:
    tot += times * int(b)
    tot %= MOD
    times *= a
    times %= MOD

ans += (tot - pow(a, l - 1, MOD) + 1) * (l - 1) % MOD
print(ans % MOD)