program fact;

{$mode objfpc}{$H+}

uses
  Classes, SysUtils
  { add your units here };

var
   p:int64;
   
procedure calc;
var
   c,i,d,z:int64;
begin
     i:=1;
     c:=0;
     d:=0;
     while (c<p) do
     begin
          c:=0;
          d:=0;
          inc(i);
          z:=i;
          while z div 5 > 0 do
          begin
               inc(c, z div 5);
               z:= z div 5;
          end;
     end;
     if (c=p) then writeln(i) else writeln('-1');
end;

begin
     assign(input,'fact.in');reset(input);
     assign(output,'fact.out');rewrite(output);
     while not eof do
     begin
          readln(p);
          calc;
     end;
     close(output);
end.