3Sum

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class Program
{
    static int[] Ria(string line = null)
    {
        line ??= Console.ReadLine();
        if (string.IsNullOrWhiteSpace(line)) return Array.Empty<int>();
        return line.Trim().Split(new[] { ' ', ',', '\t' }, StringSplitOptions.RemoveEmptyEntries)
            .Select(int.Parse).ToArray();
    }
    static string[] Rsa()
    {
        int n = int.Parse(Console.ReadLine());
        var arr = new string[n];
        for (int i = 0; i < n; i++) arr[i] = Console.ReadLine();
        return arr;
    }
    static void W(params object[] parts) => Console.WriteLine(string.Join(" ", parts));
    static void Wb(bool v) => Console.WriteLine(v ? "true" : "false");
    static void Wi(int v) => Console.WriteLine(v);
    static void Ws(string v) => Console.WriteLine(v);

    static void Main()
    {
var nums = Ria();
Array.Sort(nums);
int count = 0;
for (int i = 0; i < nums.Length; i++) {
    if (i > 0 && nums[i] == nums[i - 1]) continue;
    int l = i + 1, r = nums.Length - 1;
    while (l < r) {
        int sum = nums[i] + nums[l] + nums[r];
        if (sum == 0) { count++; l++; while (l < r && nums[l] == nums[l - 1]) l++; }
        else if (sum < 0) l++; else r--;
    }
}
Wi(count);
    }
}