program untitled;
var sol:record
     x5,x2:integer;
    end;
   n,i:longint;
procedure get_x2_x5(i:integer;var x,y:integer);
begin
 while i mod 2 = 0 do
  begin
   inc(y);
   i:=i shl 2;
  end;
 while i mod 5 = 0 do
  begin
   inc(x);
   i:=i div 5;
  end;

end;

begin
 assign(input,'fact.in');
 reset(input);
 assign(output,'fact.out');
 rewrite(output);
 readln(n);
 i:=0;
 while (sol.x5<>n) and (sol.x2<>n) do
  begin
   inc(i);
   get_x2_x5(i,sol.x5,sol.x2);
  end;
 if n>0 then writeln(i);
 close(output);
end.