A = int(input())
B = input()
DB = int(B,A)
m = len(B)
AA = 1
mod = 10 ** 9 + 7
ans = 0
for i in range(1,m):
    AA = (AA * A) % mod
    ans = (ans - AA) % mod
ans = (ans + (m-1) * AA) % mod
ans = (ans + (m -1) * (DB - AA +1)) % mod
print(ans)