#include <iostream.h>
#include <fstream.h>
ifstream fin("fact.in");
ofstream fout("fact.out");
int zero(int x)
{
	int nrzero=0;
	while (x%10==0)
	{
		nrzero=nrzero+1;
		x=x/10;
	}
	return nrzero;
}
int main()
{
	long p,fact=1;
	int n=1,ok=1;
	fin>>p;
	while (ok==1)
	{
		fact=fact*n;
		n=n+1;
		if (zero(fact)==p) ok=0;
		else ok=1;
	}
	fout<<n;
	return 0;
	fout.close();
}