#include <iostream>
#include<math.h>
#include<stdlib.h>
#include<fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int main()
{
	int P,n=1,s=0,q=5,i=5,count=0,x=5,cc=0;
	in>>P;
	while(count<P)
	{
		if (i==q)
		{
			//cout<<q;
			q=q*5;
			cc++;
			count=count+cc-1;
		}
		count++;
		//cout<<count;
		i=i+5;
	}
	if (count!=P) out<<-1;
	else out<<i-5;
}