#include <iostream>
#include <fstream>
using namespace std;
int main ()
{
 unsigned int nrzero = 0 , p , aux , n ;
 int i = 0 ;
 fstream f("fact.in",ios::in );
 f>>p ;
 aux = p * 5 ;
 n = aux ;
 f.close(); 
 for( i = 0 ; i < n ; i+= 25 ) 
 {
  while( i != 0 & i%5 == 0)
  {
   i/=5;
   if(i % 5 == 0)      
    aux-=5;
  }
 }
 fstream g ("fact1.out",ios::out );    
 if ( i == n ) 
 g << -1; 
 else        
 g << aux  ;
 g.close();
 return 0 ; 
}