Bootstrap btn-group inside form-group and border-radius

I try to remove border-radius of first child label with no success. For example, I tried with no success:

.btn-group .label:first-child {
    border-top-left-radius:0px;
}

The labels are inside btn-group which are inside form-group:

http://ift.tt/2rodKKt

How to remove first label border-radius top left and bottom left?