// Created by PhantomCracker. Copyright(c) PhantomCracker

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

long long int verificare(int n, int p)
{
	int zero;
	long long int produs = 1;
	for(int i=1; i<=n; i++)
	{
		produs *= i;
		int numar_verificare = produs;
		zero = 0;
		while(numar_verificare)
		{
			int cifra = numar_verificare%10;
			if(cifra == 0)
			{
				zero++;
				if(zero == p) return i;
			}
			else break;
			numar_verificare /= 10;
		}
	}
	return -1;
}

int main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");

	int p;
	f>>p;
	//cout<<endl<<p;
	g<<verificare(1000000, p);
	cout<<endl;
	return 0;
}