#include<fstream.h>
#include<math.h>
int multiplu(int n)
{
	int p=0;
	while(n)
	{
	  if(n%5==0)
		  p++;
	  n=n/5;
	}
	return p;
}
int i=1,j,n,k=1,s,s1,a[100];
int main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");
   f>>n;
	while(k<=n)
	{
	    if(i%5==0)
		{
			s=multiplu(i);
			k=k+s;
		}
		i++;
	}
	if(i<0)
	g<<-1;
	if(i==1)
	g<<i<<"\n";
	else
		g<<i-1<<"\n";
	return 0;
}