#include<iostream.h>
#include<fstream.h>

int main()
{
	ifstream f;
	f.open("fact.in");
	ofstream g;
	g.open("fact.out");
	long int p;
	f>>p;
	int ok=0;
	long int i=1;
	int k=0, l=0;
	while (!ok)
	{
		k=0; l=0;
		for(long int j=1;j<=i;j++)
		{	if (j%2==0) k++;
			long int aux=j;
			if(aux%5==0)
				while(aux%5==0)
				{
					aux=aux/5;
					l++;
				}
			
		}
		if ((l<=k) && (l==p)) ok=1;
			else i++;
	
	}
	if (ok) g<<i;
	else g<<"-1";
			
	return 0;
}