# Codeblock 8
class BackboneNeck(nn.Module):
    def __init__(self):
        super().__init__()
        
        self.cnn   = CNN()
        self.fpn   = FPN()
        self.panet = PANet()
    
    def forward(self, x):
        c2, c3, c4, c5 = self.cnn(x)
        print(f'c2: {c2.size()}')
        print(f'c3: {c3.size()}')
        print(f'c4: {c4.size()}')
        print(f'c5: {c5.size()}\n')
        
        p2, p3, p4, p5 = self.fpn(c2, c3, c4, c5)
        print(f'p2: {p2.size()}')
        print(f'p3: {p3.size()}')
        print(f'p4: {p4.size()}')
        print(f'p5: {p5.size()}\n')
        
        n2, n3, n4, n5 = self.panet(p2, p3, p4, p5)
        print(f'n2: {n2.size()}')
        print(f'n3: {n3.size()}')
        print(f'n4: {n4.size()}')
        print(f'n5: {n5.size()}')
        
        return n2, n3, n4, n5