代码如下

using System;
using System.Numerics;
class p1601{
    private static string a,b;
    static void Main(){
        a=Console.ReadLine();
        b=Console.ReadLine();
        Console.WriteLine(BigInteger.Parse(a)+BigInteger.Parse(b));
    }
}

运行后显示

/tmp/compiler_03nzrdel/src(8,27): error CS0103: The name `BigInteger' does not exist in the current context
Compilation failed: 1 error(s), 0 warnings

官方文档 求大佬指点