#include<iostream>
#include<fstream.h>
			   using namespace std;
				 ifstream f("fact.in");
				 ofstream g("fact.out");
unsigned long long func(unsigned long long c)
{
unsigned long long nrz=0,i=1,aux;
while(aux!=0)
{aux=c;
for(int l=1;l<=i;l++)
aux/=5;
nrz+=aux;i++;}
return nrz;
			 }
unsigned long long a=0,b=100,p,sol;
int main()
{
	f>>p;
	f.close();
int flag=1;
	do
	{
		 unsigned long long c=(a+b)/2,k=func(c);
		 if (k==p) {sol=c;flag=0;}
		 if (k<p) a=c+1;
			  else b=c-1;}
			  while(a<b);
if (flag) g<<"-1";
	else g<<sol;
   g.close();
	return 0;
	}