Concept

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

namespace CSSZMMA
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Amount of students:");
            int stud = int.Parse(Console.ReadLine());
            int allowed = 0;
            for (int i = 1; i <= stud; i++)
            {
                Console.WriteLine("Please specify name:");
                string name = Console.ReadLine();
                Console.WriteLine("Enter marks:");
                int mark1 = int.Parse(Console.ReadLine());
                int mark2 = int.Parse(Console.ReadLine());
                int mark3 = int.Parse(Console.ReadLine());
                int marksTotal = 0;
                if (mark1 > 90)
                    marksTotal += 1;
                if (mark2 > 90)
                    marksTotal += 1;
                if (mark3 > 90)
                    marksTotal += 1;
                if (marksTotal == 3)
                {
                    Console.WriteLine(name);
                    allowed += 1;
                }
            }
            Console.WriteLine("Allowed: " + allowed + " students.");
        }
    }
}