#include<fstream>
using namespace std;
int main()
{	
	long p,i,x=0,l;
	ifstream in("factorial.in");
	ofstream out("factorial.out");
	in>>p;
	while (p/25!=0)
	{x=x+125;
	i=x;
	p=p-28;
	while (i%5==0)
	{i=i/5;
	p--;}}
	l=p/6;
	i=p%6;
	if (p>=0) {if (i==0) x=x+l*25
				else x=x+l*25+i*5;}
				else x=x-(4+p)*5;
	out<<x;
	in.close();
	out.close();
	return 0;
}