def equation_of_line(values):
    b = values[0]
    k = values[1] - b
    
    if any(y != k * x + b for x, y in enumerate(values, 0)):
        return
    
    res = ""
    
    if k:
        res += f"{'-' if k == -1 else k != 1 and k or ''}x"
    
    if b:
        res += (res and " ") + "+-"[b < 0] + str(abs(b))
    return f"y = {res}"
        


v = [0, -1, -2, -3, -4]
print(equation_of_line(v))