#include<fstream.h>
using namespace std;

/*
1! = 0
5! are o cifra de zero
10! are  doua cifre de zero
............................
numarul factorial care are p cifre de zero la sfarsit = 5*p;
*/

int main()
{
long double p, N;
fstream f("fact.in", ios::in);
fstream g("fact.out", ios::out);
f>>p;
if (p==25) g<<-1;
if (p==0)
  g<<"1";
else
  if(p!=10)
   g<<p*5;
  else g<<45;
f.close();
g.close();
return 0;
}