#include <stdio.h>
#include <stdlib.h>

int fact (int n)
{
	int i, p;
	int k = 0;

	if (n == 0)
		return 1;
	
	p = 1;
	for (i = 1; i <= n; i++)
		if ((p % 10) == 0)
		{
			p = p / 10;
			k++;
			p = p * i;
		}
		else
			p = p * i;

	return k;
}

int main()
{
	int N, P;
	FILE *f, *g;
	
	f = fopen ("fact.in", "r");
	g = fopen ("fact.out", "w");

	fscanf (f, "%d", &P);

	N = 1;

	while (1)
	{
		if (fact(N) == P)
		{
			fprintf(g, "%d", N - 1);
			break;
		}
		N++;
	}	

	fclose(f);
	fclose(g);

	return 0;
}