#include <fstream.h>
int P , min , i , m , ok , div_2 , div_5 ;
int main()
{
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>P;i++;
	while(min!=P)
	{
		i++;
		m=i;
		do
		{
			ok=0;
			if(m%2==0)
			{
				div_2++;
				m/=2;
				ok=1;
			}
			if(m%5==0)
			{
				div_5++;
				m/=5;
				ok=1;
			}
		}
		while(ok==1);
        if(div_2<div_5) min=div_2;
		else min=div_5;
	}
	g<<i;
	f.close();
	g.close();
	return 0;
}