#include<fstream>
#include<climits>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
	int p,m,i=1,k,j=LONG_MAX,ok=0,x;
	fin>>p;
	if(p==0)fout<<"1";
	while(i<=j&&ok==0){
		m=(i+j)/2;
		x=5;
		k=0;
		while(x<=m){
			k=k+m/x;
			x=x*5;
		}
		if(k==p)ok=1;
		else if(k>p)j=m-1;
		else i=m+1;
	}
	if(ok==0)fout<<"-1";
	else 
	{
		while(m%5!=0)m--;
		fout<<m;
	}
}