#include <stdio.h>
#include <string.h>
#include <math.h>

int p,s;
long long t;
//--------------------------------
void read()
{
	freopen("fact.in", "rt", stdin);
	scanf("%d", &p);
}
//--------------------------------
void solve()
{
	t = (p>1? 1: 0);
	for(s=1; s<p; s++)
	{
		for(int q=s; q%5==0; q/=5)
			s++;
		t++;
	}
	if(s > p)
		t = -1;
}
//--------------------------------
void print()
{
	freopen("fact.out", "wt", stdout);
	printf("%lld\n", t*5);
}
//--------------------------------
int main(void)
{
	read();
	solve();
	print();
	return 0;
}