Httppostedfilebase.ContentLength.Tostring() returns "0"

Question

Follows code:

HttpFileCollectionBase files;

I get the file size like this:

var tamanho = files[0].ContentLength; //tamanho é 1250

So far works normal when I want to convert to string:

var tamanho = files[0].ContentLength.ToString(); //para string "0"

With ToString() returns "0". Why does that happen ?

Update:

The following code works:

var tamanho = files[0].ContentLength;
var tamanho_string = tamanho.ToString(); //funciona "1250"

When I do ToString() direct, ex:

var tamanho = files[0].ContentLength.ToString(); // "0"