Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Frontal and lateral views of the chest . Linear opacity in the left lung base most likely represents atelectasis ; otherwise , the lungs are clear and well expanded . There is no pleural effusion or pneumothorax . The cardiac and mediastinal contours appear normal . There is no free air beneath the hemidiaphragms . There are old left rib deformities .
    OUTPUT:
    
No pneumonia . No acute cardiopulmonary process .