A = int(input())
B = input()
l = list(map(int,list(B)))
n = len(l)
ans = 0
P = 10 ** 9 + 7
b = 0
beki = 1
for i in range(n):
    tmp = beki * A % P
    if i < n - 1:
        ans += (tmp - beki) % P * i % P
        ans %= P
    b = (b + beki * l[-1-i]) % P
    if i == n-1:
        ans = (ans + (b - beki + 1)*i) % P
    beki = tmp
print(ans)