#include <fstream>
#include <cmath>
#include <iostream>
int main()
{
  std::ifstream in("fact.in");
  std::ofstream out("fact.out");
  int numar, nrDeCifreFact = 1;
  in >> numar;
  if (numar < 0) nrDeCifreFact = -1;
  else if (numar <= 1) nrDeCifreFact = 1;
  else {
    double x = ((numar * std::log10(numar / M_E) +
	       std::log10(2 * M_PI * numar) / 2.0));
    nrDeCifreFact = std::floor(x) + 1;
  }
  out << nrDeCifreFact << '\n';
  return 0;
}