階乗の桁数と末尾0の個数

a.cpp

#include <iostream>
#include <cmath>
using namespace std;

typedef long long ll;

int main() {
  ll n;
  cin >> n;

  ll tmp = n;
  ll zero = 0;
  while (tmp >= 5) {
    zero += tmp / 5;
    tmp /= 5;
  }

  double keta = n * (log10((double)n)-0.43429448190325) + 0.5*log10(M_PI*2.0*n);
  cout << int(keta)+1 << " " << zero << endl;

  return 0;
}