ContrastiveLoss Layer takes 3 vs. 4 bottom blob(s) as input?

My ContrastiveLoss Layer is as flows like you:

layer {
name: "loss"
type: "ContrastiveLoss"
bottom: "fc6_1"
bottom: "fc6_2"
bottom: "label_1"
bottom: "label_2"
top: "fc6_loss"
contrastive_loss_param{
margin: 0
}
loss_weight: 0.001
}

but it occurs the following error messages:

Check failed: ExactNumBottomBlobs() == bottom.size() (3 vs. 4) ContrastiveLoss Layer takes 3 bottom blob(s) as input.

So I want to know if do you have the same problem?