#include<iostream.h>
#include<fstream.h>
#include<math.h>
long unsigned determinare_putere(long unsigned n)
{long unsigned k=0,p=1;
 while(p<n)
  {p=p*5;k++;}
 return k;
}
long unsigned numar_zerou(long unsigned n)
{
 long unsigned suma=0,i,p,j;
 for(i=1;i<=determinare_putere(n);i++)
  {p=1;
	for(j=1;j<=i;j++)
	 p=p*5;
	suma=suma+(n/p);};
 return suma;
}
int main()
{long unsigned P,i=0;
 ifstream f("fact.in");
 ofstream g("fact.out");
 f>>P;
 if(P==0)
  g<<1;
 else
 if(P!=0)
 { do
  {i=i+5;}
  while(numar_zerou(i)<P);
 g<<i;}
 f.close();g.close();return 0;}