#include <fstream.h>


unsigned long int p;



int main()
{
	ifstream fin("fact.in");
	ofstream fout("fact.out");

	fin >> p;

	unsigned long int nr = 0;
	unsigned long int n = 1;
	int ok = 1;
	int numar = 0;


	while (ok)
	{
		if (p == 0)
			break;
		nr = 0;
		for (unsigned long int i = 1; i < n; i++)
		{
			numar = i;
			while (numar)
			{
				if (numar %5 == 0)
					nr++;
				else break;
				numar /=5;
			}
		}

		if (nr == p)
		{
			ok = 0;
			break;
		}
		n++;

	}

	fout << n-1;

	fin.close();
	fout.close();
	return 0;
}