import sys
import struct

def get_ogg_opus_duration(filepath):
    with open(filepath, 'rb') as f:
        f.seek(0, 2)
        file_size = f.tell()
        
        # Read the last 65536 bytes (or file size if smaller) to find the last Ogg page
        chunk_size = min(65536, file_size)
        f.seek(file_size - chunk_size)
        data = f.read(chunk_size)
        
        # Find the last 'OggS' magic number
        last_oggs_idx = data.rfind(b'OggS')
        if last_oggs_idx == -1:
            return 0
        
        # Read the granule_position (absolute granule position) which is 8 bytes at offset 6
        granule_bytes = data[last_oggs_idx+6 : last_oggs_idx+14]
        granule_position = struct.unpack('<q', granule_bytes)[0]
        
        # Opus sample rate is always 48000 for granule position purposes
        duration_ms = int((granule_position / 48000.0) * 1000)
        return duration_ms

if __name__ == '__main__':
    print(get_ogg_opus_duration(sys.argv[1]))