#include<fstream.h>
				 ifstream f("factorial.in");
				 ofstream g("factorial.out");
unsigned long long func(unsigned long long c)
{
unsigned long long nrz=0,i=1,aux,l;
while(aux!=0)
{
	aux=c;
for(l=1;l<=i;l++)
	aux/=5;
nrz+=aux;i++;}
return nrz;
			 }
int main()
{
unsigned long long a=0,b=100000,p;
	f>>p;
	f.close();
int flag=1;
	do
	{
		 unsigned long long c=(a+b)/2;
		 if (func(c)==p) {g<<p;flag=0;break;}
		 else if (func(c)>p) b=c-1;
			  else a=c+1;}
			  while(a<=b);
if (flag) g<<"-1";     
   g.close(); 
	return 0;
	}