def rolling_average(values, window):
    if window <= 0:
        raise ValueError("Window size must be greater than zero")
    if len(values) < window:
        return []
    result = []
    for i in range(len(values) - window + 1):
        window_slice = values[i:i + window]
        result.append(sum(window_slice) / window)
    return result
