#include<iostream.h>
#include<fstream.h>
long i,p,pr,s;
 ifstream fin("fact.in");
 ofstream fout("fact.out");
int main()
{
	fin>>p;
	if(i==0) fout<<1<<endl;
	else
	{
	 i=5;
	 do
	 {
		s=0;
		pr=1;
		i=i+5;
		do
		{
			pr=pr*5;
			s=s+i/pr;
		}
		while(pr<=i);
	 }
	 while(s<p);
	}
	fout<<i<<endl;
return 0;
}