#include<iostream.h>
#include<fstream.h>
                 //using namespace std;
                 ifstream f("factorial.in");
                 ofstream g("factorial.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;             
             }
int main()
{
unsigned long long a=0,b=100,p;    
    f>>p;
    f.close();
int flag=1;
    do
    {
         unsigned long long c=(a+b)/2;
         if (func(c)==p) {g<<p;flag=0;break;}
         else if (func(c)>p) b=c-1;
              else a=c+1;}
              while(a<=b);
if (flag) g<<"-1";     
   g.close(); 
	return 0;
	}