#include <iostream>
#include <fstream>

using namespace std;

int lol(int x, int y)
{
	if(x % 5 != 0)
		return y;
	else
	{
		y++;
		return lol(x / 5, y);
	}
} 
	
int main()
{
	ifstream fin("fact.in");
	ofstream fout("fact.out");
	int a, k;
	fin >> a;
	int b;
	int suma = 0;
	int j = 1;
	while (suma < a)
	{
		k = 1;
		b = lol(j, k);
		suma += b;
		j++;
	}   
	if(a == 0)
		fout << 1;
	else
		if (suma == a) 
			fout << ((j-1) * 5);
		else
			fout << "-1";
	fin.close();
	fout.close();
	return 0;
}