#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
unsigned long long put5[25];
unsigned long long v[25];
unsigned long long p;
int cautare_binara(unsigned long long v[], int st,int dr)
{
	if(st==dr)
		return 0;
	int mij=(st+dr)/2;
	if(v[mij]==p)
		return mij;
	else
		if(v[mij]>=p)
			return cautare_binara(v,st,mij);
		else
			return cautare_binara(v,mij+1,dr);
}
int main()
{
	put5[1]=1;
	for(int i=2;i<=24;i++)
	{
		put5[i]=put5[i-1]*5;
	}
	v[1]=1;
	for(int i=2;i<=24;i++)
	{
		v[i]=v[i-1]+put5[i];
	}
	f>>p;
	int gasit=0;
	gasit=cautare_binara(put5,1,25);
	if(gasit)
		g<<"-1\n";
	else
	{
		gasit=cautare_binara(v,1,25);
	}
	return 0;
}