furui = {}
primes = {}
-- get primes
n = io.read("*n")
for i = 2, n do
  if(not furui[i]) then
    table.insert(primes, i)
    jmax = math.floor(n / i)
    for j = 2, jmax do
      furui[j * i] = true
    end
  end
end
-- do DP
sumbox = {}
cursum = 0
sumbox[0] = 0
-- for i = 1, n do sumbox[i] = -1 end
for k, v in pairs(primes) do
  for i_sum = cursum, 0, -1 do
    if(sumbox[i_sum] ~= nil) then
      if(sumbox[i_sum + v] == nil) then
        sumbox[i_sum + v] = sumbox[i_sum] + 1
      else
        sumbox[i_sum + v] = math.max(sumbox[i_sum] + 1, sumbox[i_sum + v])
      end
    end
  end
  cursum = math.min(n, cursum + v)
end
if(sumbox[n] == nil) then print("-1") else print(sumbox[n]) end