A = int(input())
B = int(input())
B= int(str(B),A)
i = 0
x = 1
j = A
ans = 0
mod = 10 ** 9 + 7
while x * A <= B:
    ans = (ans + (A-1) * x * i) % mod
    i += 1
    x *= A
ans = (ans + (B - x + 1) * i) % mod

print(ans)