import torch.nn as nn
from torchvision import models

def build_model(num_classes):
    model = models.mobilenet_v2(weights=models.MobileNet_V2_Weights.DEFAULT)
    model.classifier[1] = nn.Sequential(
        nn.Linear(model.last_channel, 128),
        nn.ReLU(),
        nn.Dropout(0.5),
        nn.Linear(128, num_classes)
    )
    return model