#include<fstream>
using namespace std;
FILE*in;
ofstream out("fact.out");
int f, i, nr0, p, j, x;
bool JACK=true;
int main()
{
	in=fopen("fact.in","r");
	fscanf(in,"%d",&p);
	j=1;
	while(JACK)
	{
		f=1;
		nr0=0;
		for (i=1; i<=j; i++)
			f*=i;
		x=f;
		while (x)
			if (x%10==0)
			{
				nr0++;
				x/=10;
			}
			else
				break;
		if (nr0==p)
			JACK=false;
		else
			j++;
	}
	out<<j;
	return 0;
}