import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws IOException {
		Scanner in = new Scanner(new FileInputStream("fact.in"));
        PrintWriter out = new PrintWriter("fact.out");
  
        int p = in.nextInt();
        int pow = 1;
        int lg = 0;
        while(pow*5 <= p) {
        	pow *=5;
        	++lg;
        }
        
        if(pow == p && p != 1) {
            out.printf("%d%n", -1);
        } else {
            out.printf("%d%n", 5*(p-(lg*(lg+1))/2) + (p==0?1:0));
        }
  
        in.close();
        out.close();
	}
}