#include<iostream>
#include<fstream>
//#include<windows.h>
using namespace std;

ifstream in;
ofstream out;

long int mini(long int a, long int b)
{
	if (a > b)
		return b;
	else
		return a;
}

int main() {
	bool a = true;
	long int P, nr2=0, nr5=0;
	long long int	N=0, i=0, n=0, m;

	in.open("fact.in");
	in >> P;
	in.close();
	
	/*while (a){
		N++;
		n = N;
		while (n % 2 == 0)
		{
			nr2++;
			n /= 2;
		}
		while (n % 5 == 0)
		{
			nr5++;
			n /= 5;
		}
		if (mini(nr2, nr5) >= P)
		{
			a = false;
		}
	}	*/
	if (P == 0)
	{
		N = 1;
	}
	else
	{
		while (a)
		{
			N += 5;
			i++;
			n++;
			m = i;
			while (m % 5 == 0)
			{
				n++;
				m /= 5;
			}
			if (n >= P)
			{
				a = false;
			}
		}
	}
	

	out.open("fact.out");
	out << N;
	out.close();
	//system("pause");
}