#include <fstream.h>
int main ()
{long i,s,j,p;
ifstream f("fact.in");
ofstream g("fact.out");
f>>p;
for (i=p*4;i<=p*5;i=i+5)
	{s=0;
	for (j=5;j<=i;j=j*5)
		s=s+i/j;
	if(s>p) {g<<-1; break;}
	else if (s==p) {g<<i/5*5; break;}
	}
return 0;
}