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import sys

ERR = (28, 29)

def build_log():
    lines = []
    for i in range(40):
        if i in ERR:
            lines.append(f"{i:04d} ERROR dma timeout on channel {i - 27}")
        elif i % 9 == 4:
            lines.append(f"{i:04d} WARN temperature {70 + i} C")
        else:
            lines.append(f"{i:04d} INFO heartbeat ok")
    return lines

def trim(lines, before=3, after=5):
    keep = set()
    for i, ln in enumerate(lines):
        if "ERROR" in ln:
            for j in range(i - before, i + after + 1):
                if 0 <= j < len(lines):
                    keep.add(j)
    return sorted(keep)

def main():
    lines = build_log()
    kept = trim(lines)
    bad = 0
    if len(lines) != 40:
        bad += 1
    if kept != list(range(25, 35)):
        bad += 1
    if not all(i in kept for i in ERR):
        bad += 1
    if not (len(kept) < len(lines)):
        bad += 1
    if bad == 0:
        print(f"PASS: kept {len(kept)} of {len(lines)} lines around {len(ERR)} flagged lines")
    else:
        print(f"FAIL: {bad} checks wrong")
        sys.exit(1)

main()