c# 判断某个数字在某个范围 ,如何做,

//using System.Linq;
static void Main(string[] args)
{
//Dictionary
Dictionary D = new Dictionary();
D.Add("1001", "100000-199999");
D.Add("1002", "200000-299999");
D.Add("1003", "300000-399999");
//int i=100001;//1001
int i = 399998;//1003
var d = D.First(x =>
Convert.ToInt64(x.Value.Split(new char[] { '-' })[0]) <= i &
Convert.ToInt64(x.Value.Split(new char[] { '-' })[1]) >= i
).Key;
Console.WriteLine(d);
Console.ReadLine();
}