import std.algorithm, std.conv, std.range, std.stdio, std.string;

void main()
{
  auto n = readln.chomp.to!int;
  auto p = primes(n);

  auto dp = new int[](n+1); dp[0] = 1;
  foreach (i, pi; p)
    foreach_reverse (j; pi..n+1)
      if (dp[j-pi]) dp[j] = max(dp[j], dp[j-pi]+1);

  writeln(dp[n] ? dp[n]-1 : -1);
}

pure T[] primes(T)(T n)
{
  import std.algorithm, std.bitmanip, std.conv, std.range;

  auto sieve = BitArray();
  sieve.length((n + 1) / 2);
  sieve = ~sieve;

  foreach (p; 1..((nsqrt(n) - 1) / 2 + 1))
    if (sieve[p])
      for (auto q = p * 3 + 1; q < (n + 1) / 2; q += p * 2 + 1)
        sieve[q] = false;

  auto r = sieve.bitsSet.map!(to!T).map!("a * 2 + 1").array;
  r[0] = 2;

  return r;
}

pure T nsqrt(T)(T n)
{
  import std.algorithm, std.conv, std.range, core.bitop;
  if (n <= 1) return n;
  T m = 1 << (n.bsr / 2 + 1);
  return iota(1, m).map!"a * a".assumeSorted!"a <= b".lowerBound(n).length.to!T;
}