local mod = 1000000007
local mfl = math.floor

local function bmul(x, y)
  local x1, y1 = mfl(x / 31623), mfl(y / 31623)
  local x0, y0 = x - x1 * 31623, y - y1 * 31623
  return (x1 * y1 * 14122 + (x1 * y0 + x0 * y1) * 31623 + x0 * y0) % mod
end

local function badd(x, y)
  return (x + y) % mod
end

local function bsub(x, y)
  return x < y and x - y + mod or x - y
end

local function modpow(src, pow)
  local res = 1
  while 0 < pow do
    if pow % 2 == 1 then
      res = bmul(res, src)
      pow = pow - 1
    end
    src = bmul(src, src)
    pow = mfl(pow / 2)
  end
  return res
end

local a = io.read("*n", "*l")
local s = io.read()
local sn = #s
local ret = 0
local v = 0
local b = {1}
for i = 2, sn do
  b[i] = bmul(b[i - 1], a)
end
for i = 1, sn do
  v = badd(bmul(v, a), s:byte(i) - 48)
end
local mul = 1
for i = sn, 2, -1 do
  mul = bmul(mul, a)
  local z = bsub(mul, 1)
  ret = badd(ret, bsub(v, z))
end
print(ret)