#include<fstream>
using namespace std;
int main()
{	int p,n;
	ifstream in("fact.in");
	ofstream out("fact.out");
	in>>p;
	if(p==0) out<<1<<"\n";
	     else if(p%2==0) 
				{
					n=p/2;
					n*=10;
					out<<n<<"\n";
				 }			 
			 else if(p%2==1)
				{
					n=p/2;
					n*=10;
					n+=5;
					out<<n<<"\n";
				}
				
	in.close();
	out.close();
	return 0;
}