your model is not a valid java name

Hello, I'm new to this mod making thing.

I was trying to make a simple model for a mod in blockbench and when I tried to put the java model file in it said your model name is not a valid java name. I looked it up on the forums, and the solutions wouldn't help me. 

Code in the java file:

// Made with Blockbench 3.7.5
// Exported for Minecraft version 1.12
// Paste this class into your mod and generate all required imports

public class custom_model extends ModelBase {
    private final ModelRenderer head;

    public custom_model() {
        textureWidth = 48;
        textureHeight = 48;

        head = new ModelRenderer(this);
        head.setRotationPoint(0.0F, 24.0F, 0.0F);
        head.cubeList.add(new ModelBox(head, 24, 9, -8.0F, -30.0F, 1.0F, 8, 8, 1, 0.0F, false));
        head.cubeList.add(new ModelBox(head, 14, 14, -1.0F, -30.0F, 2.0F, 1, 8, 6, 0.0F, false));
        head.cubeList.add(new ModelBox(head, 24, 0, -8.0F, -30.0F, 8.0F, 8, 8, 1, 0.0F, false));
        head.cubeList.add(new ModelBox(head, 0, 14, -8.0F, -30.0F, 2.0F, 1, 8, 6, 0.0F, false));
        head.cubeList.add(new ModelBox(head, 0, 7, -7.0F, -30.0F, 2.0F, 6, 1, 6, 0.0F, false));
        head.cubeList.add(new ModelBox(head, 0, 0, -7.0F, -23.0F, 2.0F, 6, 1, 6, 0.0F, false));
    }

    @Override
    public void render(Entity entity, float f, float f1, float f2, float f3, float f4, float f5) {
        head.render(f5);
    }

    public void setRotationAngle(ModelRenderer modelRenderer, float x, float y, float z) {
        modelRenderer.rotateAngleX = x;
        modelRenderer.rotateAngleY = y;
        modelRenderer.rotateAngleZ = z;
    }
}

Please help.