我一直在努力在MonoDevelop中添加BigInteger以允许非常大的数字，然而System.Numerics给我带来了很多麻烦。我已经添加了.dll引用，iv 'e确保所有其他内容都被正确引用，但我仍然得到这个错误：

Assets/Scripts/Click.cs(4,14): error CS0234: The type or namespace name `Numerics' does not exist in the namespace `System'. Are you missing an assembly reference?

下面是我尝试使用Numerics的类：

using UnityEngine;
using System.Collections;
using System;
using System.Numerics;

public class Click : MonoBehaviour {

    public UnityEngine.UI.Text PixelsDisplay;
    public UnityEngine.UI.Text PPC;
    public double pixels = 0.0;
    public double ppc = 1.0; 

    void Update(){
        PixelsDisplay.text = "Pixels: " + pixels.ToString ("#,#");
        if (pixels >= 10000000) {
            PixelsDisplay.text = "Pixels: " + Math.Round(pixels / 1000000, 2) + "M";
        }
        if (pixels >= 1000000000) {
            PixelsDisplay.text = "Pixels: " + Math.Round(pixels / 1000000000, 2) + "B";
        }
        if (pixels >= 1000000000000) {
            PixelsDisplay.text = "Pixels: " + Math.Round(pixels / 1000000000000, 2) + "T";
        }
        if (pixels >= 1000000000000000) {
            PixelsDisplay.text = "Pixels: " + Math.Round(pixels / 1000000000000000, 2) + "Qd";
        }
        if (pixels >= 1000000000000000000) {
            PixelsDisplay.text = "Pixels: " + Math.Round(pixels / 1000000000000000000, 2) + "Qt";
        }
        if (pixels >= BigInteger.Parse("1000000000000000000000")) {
            PixelsDisplay.text = "Pixels: " + Math.Round(pixels / BigInteger.Parse("1000000000000000000000"), 2) + "Sx";
        }

        PPC.text = "PPC: " + ppc.ToString ("#,#");
        //TODO
    }

    public void Clicked(){
            pixels += ppc;
    }
}

下面是一张图片，展示了我所有的参考资料：

我搜索过类似的问题，但给出的答案不直接处理System.Numerics，通常不使用MonoDevelop。谢谢你的帮助！