#include <iostream>
#include <fstream>
using namespace std;
ifstream fi("fact.in");
ofstream fo("fact.out");
long p,n;
int nrcifre(long n){
long	k=0;
	while(n){
		n/=10;
		k++;
	}
	return k;
}
int putere(long n){
	long k=1,i;
	for(i=1;i<=n;i++) k*=10;
	return k;
}
int main(){
	fi>>p;
	if(p==0) n=1;
	if(p>0&&p>=10) n=p*5-(p/(putere(nrcifre(p)-1)))*5;
	fo<<n;
}