using System.Collections.Generic;
public static void Main()
List<int> a = new List<int>(){-2,1,3,-4,5,15,-17,13};
List<int> c= new List<int>();
b = b.Where(j => j != a[prev]).ToList();
int sum = b.Sum(k => Convert.ToInt32(k));
Console.WriteLine(ressum);