#include <fstream>  
   using namespace std;  
   ifstream f1 ("fact.in");  
   ofstream f2 ("fact.out");
   int fact (int x)
     {int w=0;
      while (x%5==0) {w++; x/=5;}
      return w;}   
   int main()  
   {  
   long  n,p,r,q,m;  
   f1>>p; f1.close();  
   r=p;  
   n=0;  
   while (r>0)  
    {n=n+5;  
     q=fact(n);     
     r=r-q;}  
   if (p!=0)  
   {if (r==0) f2<<n;  
    else f2<<"-1";}  
       else f2<<1; f2.close();  
   }