#include <stdio.h>

long n, nr;

void cit()
{
	FILE *f=fopen("fact.in", "r");
	fscanf(f, "%ld", &n);
	fclose(f);
}
long put5(long nr)
{
	long i=0;
	while (nr%5==0)
	{
		nr/=5;
		i++;
	}
	return i;
}

void fact()
{
	long i;
	nr=0;
	i=0;
	while (nr<n)
	{
		i+=5;
		nr+=put5(i);
	}
	if (nr>n) nr=-1;
	if (n==0) nr=1;
}

void tip()
{
	FILE *f=fopen("fact.out", "w");
	fprintf(f, "%ld\n", nr);
	fclose(f);
}

int main()
{
	cit();
	fact();
	tip();
	return 0;
}