Largest product in a series...

Problem 8 Project Euler 

The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.

73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {
    static void Main(String[] args) {
        int t = Convert.ToInt32(Console.ReadLine());
        for(int a0 = 0; a0 < t; a0++){
            string[] tokens_n = Console.ReadLine().Split(' ');
            int n = Convert.ToInt32(tokens_n[0]);
            int k = Convert.ToInt32(tokens_n[1]);
            string num = Console.ReadLine();
            Console.WriteLine(StringToList(num,n,k));
        }
    }
    
    static long StringToList(string n, int len , int subLen)
    {
        long max=long.MinValue;
        for(var i=0; i< len-subLen; i++)
        {
           long p = ProdcutOfDigit(n.Substring(i,subLen));
           if(p > max)
               max =p;
        }
        return max;
    }
    
    static long ProdcutOfDigit(string n)
    {
        long m =1;
        var arr = n.ToCharArray().ToList().Select(s=>Convert.ToInt64(s.ToString())).ToList();
        foreach(var i in arr)
            m*=i;
        return m;
    }
}

Live Code on Ide One