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