#include<fstream.h>
int main()
{
long long p,n;
ifstream in("fact.in");
ofstream out("fact.out");
	in>>p;
if(p==0)
	n=1;
if(p>=1&&p<=5)
	n=p*5;
if(p>=6&&p<=26)
	n=(p-1)*5;
if(p>=27&&p<=627)
	n=(p-2)*5;
if(p>=628&&p<=3128)
	n=(p-3)*5;
if(p>=3129&&p<=15629)
	n=(p-4)*5;
if(p>=15630&&p<=78130)
	n=(p-5)*5;
if(p>=78131&&p<=390631)
	n=(p-6)*5;
if(p>=390632&&p<=1953132)
	n=(p-7)*5;
if(p>=1953133&&p<=9765633)
	n=(p-8)*5;
if(p>=9765634&&p<=48828134)
	n=(p-9)*5;
if(p>=48828135&&p<=100000001)
	n=(p-10)*5;

out<<n;





in.close();
out.close();
return 0;
}