#include <stdio.h>

FILE* f;

int p;
int zecimale=0;

int main()
{
	f=fopen ("fact.in","r");
	fscanf (f,"%d",&p);
	fclose (f);

	int i=1;
	int j;
	while (zecimale<p)
	{
		j=i;
		while (j%5==0)
		{
			zecimale++;
			j=j/5;
		}

		i++;
	}

	f=fopen ("fact.out","w");

	if (p!=0)
		fprintf (f,"%d",i-1);
	else
		fprintf (f,"%d",1);

	fclose (f);

	return 0;
}