MOD = 10 ** 9 + 7
a = int(input())
b = input()
ans = 0
d = a - 1
for k in range(len(b) - 1):
    ans = (ans + k * d) % MOD
    d = d * a % MOD
x = int(b[0]) - 1
for c in b[1:]:
    x = (a * x + int(c)) % MOD
ans = (ans + (len(b) - 1) * (x + 1)) % MOD
print(ans)