#include<fstream.h>
ifstream f("fact.in");
ofstream g("fact.out");
long n,p,q;
int gasit,s;
int main()
{
	f>>p;
	q=pow(10,p);
	s=1;
	n=0;
	gasit=0;
	while ( !gasit )
	  { n++;
	   s=s*n;
	   if ( s%q==0 )
		  { g<<n-1;
	        gasit=1;}
	  }
    f.close();
    g.close();
    return 0;
}