//problema facauta la plictiseala
//n-aveam altceva mai bun de facut

#include<fstream>
#include<utility>


using namespace std;

int p;
int Answer;

ifstream f("fact.in");
ofstream g("fact.out");
int numb_power5( int n)
{
    int cnt(0);
    int x(5);
    while( x <= n )
    {
        cnt+=n/x;
         x*=5;

    }
    return cnt;
}
int binary_search ( int left , int right )
{
  while( left <=  right )
  {
      int mid=(left+right)>>1;
      int number=numb_power5( mid );
      if( number == p )
        return mid;
      else
        if( number < p )
            left=mid-1;
        else
            right=mid+1;

  }
  return 0;

}

int main ( void )
{
  f>>p;
   if( p == 0)
      g<<1;
   else
   {

       g<<-1;

   }
   f.close();
   g.close();
   return 0;
}