def ClassicRK(x0,y0,h,xk,fxy):
    k1=k2=k3=k4=0
    result = [(x0,y0)]
    while x0<=xk:
        k1 = fxy(x0,y0)
        k2 = fxy(x0+h/2,y0+h*k1/2)
        k3 = fxy(x0+h/2,y0+h*k2/2)
        k4 = fxy(x0+h,y0+h*k3)
        y0 += h*(k1+4*k2+k3)/6
        x0 += h
        result.append((x0,y0))
    return result


if __name__=="__main__":
    x0 = 0
    y0 = -1
    fxy = lambda x,y: x + y
    real_fx = lambda x: -x-1
    h = 0.1
    xk = 2
    result = ClassicRK(x0, y0, h, xk, fxy)
    print("x\ty\t\treal_y")
    for x, y in result:
        print(f"{x:.2f}\t{y}\t{real_fx(x)}")