#include<fstream>
#include<iostream>

using namespace std;

long zeros(long n)
{
    long i,j=0,nr=0;

	for(i=5;i<=n;i+=5)
        {
            j++;
            nr++;
            if(j%5==0) nr+=j/5;
        }
        return nr;
}

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

	long p;
	f>>p;
	for(long i=1; ;i++)
	if(zeros(i)==p)
	{g<<i; break;}



	f.close();
	g.close();


}