using System;

class Progran
{
    public static void Main()
    {
        int Size = int.Parse(Console.ReadLine());
        sbyte[] FirstNumber = new sbyte[Size + 1];

        for (int i = 0; i < Size; i++)
        {
            string[] s = Console.ReadLine().Split(' ');
            FirstNumber[i + 1] = (SByte)(sbyte.Parse(s[0]) + sbyte.Parse(s[1]));
        }

        for (int i = Size; i > 0; i--)
            if (FirstNumber[i] >= 10)
            {
                FirstNumber[i - 1]++;
                FirstNumber[i] -= 10;
            }

        for (int i = 0; i < Size; i++)
                Console.Write(FirstNumber[i + 1]);

    }
}

Edited by author 31.05.2022 12:17

I ported this code to c++ and got AC ?!

Edited by author 31.05.2022 15:01

I finally got accepted it on a C#!! Main memory issue here are always any Strings! Awoid using Console.ReadLine() in cycle. For some reason, .net sometimes does not use string interning. I got below accepted using only Console.Read() byte-by-byte:

class Program
    {
        static int N = 0;
        static byte[] Digs1 = null;
        static char m_Zero = '0';

        static void _ReadData()
        {
            string v_Str = Console.ReadLine();
            if (v_Str == null) return false;
            N = Int32.Parse(v_Str);
            Digs1 = new byte[N];
            int v_TmpVal = 0;

            // Fill Digs
            for (int i = 0; i < N; i++)
            {
                v_TmpVal = Console.Read();
                Digs1[i] = (byte)(Convert.ToChar(v_TmpVal) - m_Zero);
                Console.Read();
                v_TmpVal = Console.Read();
                Digs1[i] += (byte)((Convert.ToChar(v_TmpVal) - m_Zero) * 10);
                Console.Read(); //#13
                Console.Read(); //#10
            }
static void SolveProblem()
        {
            bool v_AddOne = false;
            bool v_NextAddOne = false;
            byte v_First = 0;
            byte v_Second = 0;

            for (int i = Digs1.Length - 1; i >= 0; i--)
            {
                v_First = (byte)(Digs1[i] % 10);
                v_Second = (byte)(Digs1[i] / 10);

                v_AddOne = (v_First + v_Second + (v_NextAddOne ? 1 : 0)) > 9;

                Digs1[i] = (byte)((v_First + v_Second + (v_NextAddOne ? 1 : 0)) % 10);
                v_NextAddOne = v_AddOne;
            }
        }
 static void Main(string[] args)
        { _ReadData(); SolveProblem();

            for (int i = 0; i < N; i++)
            {
                Console.Write(Digs1[i]);
            }
}

Hi, I`m happy for you. And it`s great that you are sharing your thoughts.
However, you are not helping anyone by posting your code.
Please don`t do it, and we all will be happier.