#include <fstream>
using namespace std;

int cifrezero(int a)
{
	int  d = a%10, nr = 0;
	while(d == 0)
	{
		a = a/10;
		d = a%10;
		nr++;
	}
	return nr;
}

int fact(int a)
{
	int fact = 1;
	for(int i = 2; i<=a; i++)
		fact = i*fact;
	return fact;
}

int main() 
{
	int p,i = 1;
	ifstream f("fact.in");
	ofstream g("fact.out");
	f>>p;
	while(cifrezero(fact(i)) != p)
		i++;
	g<<i;
	
	return 0;
}