#include <fstream.h>  
  ifstream f("fact.in");  
  ofstream g("fact.out");  
  long n,i,nr,y,p,p1;  
  int main ()  
  {  
  f>>p1;  
     
  n=5;  
   if (p1==0)  
        g<<"1\n";  
        else  
        {  
     
   do  
   {  
   nr=0;  
   p=5;  
   y=n;  
   while (y>=p)  
               {  
               nr=nr+y/p;  
               p=p*5;  
               }  
   if (nr<p1)  
           n=n+5;  
  }  
 while (nr<p1);  
 if (nr==p1)  
       g<<n<<'\n';  
     else  
     g<<"-1\n";  
   }  
 f.close ();  
 g.close ();  
  return 0;  
  }