# Codeblock 11
class DetectionHead(nn.Module):
    def __init__(self, num_channels):
        super().__init__()
        
        self.convhead0 = Convolutional(in_channels=num_channels,
                                       out_channels=num_channels*2,
                                       kernel_size=3)
        
        self.convhead1 = nn.Conv2d(in_channels=num_channels*2, 
                                   out_channels=NUM_PRIORS*(NUM_CLASS+5), 
                                   kernel_size=1)
        
    def forward(self, x):
        print(f'original\t: {x.size()}')
        
        x = self.convhead0(x)
        print(f'after convhead0\t: {x.size()}')
        
        x = self.convhead1(x)
        print(f'after convhead1\t: {x.size()}')
   
        return x