#include<iostream>
#include<fstream>
using namespace std;
int main()
{

	int n,nr=0,p,i,aux;
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	n=1;
	while(nr!=p)
	{	n++;
		nr=0;
		for(i=1;i<=n;i++)
		{	aux=i;
			while(aux)
			{	if(aux%5==0)
					nr++;
				else
					break;
				aux=aux/5;
			}
		}
	}
	
	
	g<<n;
	f.close();
	g.close();
	 
	return 0;
}