#include <cstdio>
using namespace std;

long long fact(long long x)
{
	int p=5,nr=0;
	while (p<=x)
	{
	nr=nr+x/p;
	p=p*5;
	}
	return nr;
}

int main()
{
	freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
	long long p,f,ls=0,ld=10000000000,m;
	scanf("%lld",&p);
    while (ls<=ld)
	{
		m=(ls+ld)/2;
		if (m<5) f=0;
			else f=fact(m);
		if (f<p) ls=m+1;
			else ld=m-1;
	}
	if (fact(ls)==p) printf("%lld",ls);
	else printf("%d",-1);
	return 0;
}