#include<fstream.h>
#include<math.h>
ifstream f("fact.in");
ofstream g("fact.out");
long long n,p,i,t,s,d,gasit,z;
int main()
{
	f>>p;
	gasit=0;s=1;d=2147483647;
	while(s<=d&&gasit==0)
	{n=(s+d)/2;i=1;z=0;
	while(pow(5,i)<=n)
		{t=pow(5,i);
		z=z+n/t;
		i++;}g<<z<<'\n';
	if(z==p) gasit=1;
	else if(z<p) s=n+1;
			else d=n-1;}
	if(gasit==1) g<<n;
			else g<<"-1";
	f.close(); g.close();
	return 0;
}