Problem:
Score : 600 points

Problem Statement

There is a grid with N rows and N columns of squares. Let (i, j) be the square at the i-th row from the top and the j-th column from the left.

Each of the central (N-2) \times (N-2) squares in the grid has a black stone on it.
Each of the 2N - 1 squares on the bottom side and the right side has a white stone on it.

Q queries are given. We ask you to process them in order.
There are two kinds of queries. Their input format and description are as follows:

1 x: Place a white stone on (1, x). After that, for each black stone between (1, x) and the first white stone you hit if you go down from (1, x), replace it with a white stone.

2 x: Place a white stone on (x, 1). After that, for each black stone between (x, 1) and the first white stone you hit if you go right from (x, 1), replace it with a white stone.

How many black stones are there on the grid after processing all Q queries?

Constraints

3 \leq N \leq 2\times 10^5

0 \leq Q \leq \min(2N-4,2\times 10^5)

2 \leq x \leq N-1

Queries are pairwise distinct.

Input

Input is given from Standard Input in the following format:

N Q
Query_1
\vdots
Query_Q

Output

Print how many black stones there are on the grid after processing all Q queries.

Sample Input 1

5 5
1 3
2 3
1 4
2 2
1 2

Sample Output 1

1

After each query, the grid changes in the following way:

Sample Input 2

200000 0

Sample Output 2

39999200004

Sample Input 3

176527 15
1 81279
2 22308
2 133061
1 80744
2 44603
1 170938
2 139754
2 15220
1 172794
1 159290
2 156968
1 56426
2 77429
1 97459
2 71282

Sample Output 3

31159505795

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using System.Numerics;
using System.Threading;
using System.Runtime.CompilerServices;
using System.Diagnostics;
using static System.Math;
using static System.Array;
using static AtCoder.Cout;
using static AtCoder.Tool;
using static AtCoder.Graph;
using static AtCoder.ModInt;
namespace AtCoder
{
    class AC
    {
        //const int MOD = 1000000007;
        const int MOD = 998244353;
        const int INF = int.MaxValue / 2;
        const long SINF = long.MaxValue / 3;
        static readonly int[] dI = { 0, 1, 0, -1, 1, -1, -1, 1 };
        static readonly int[] dJ = { 1, 0, -1, 0, 1, 1, -1, -1 };
        static void Main(string[] args)
        {
            //var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }; Console.SetOut(sw);

            /*var th = new Thread(Run, 1 << 26);
            th.Start();
            th.Join();*/

            Run();
            Console.Out.Flush();
        }
        static void Run()
        {
            int Testcase = 1;
            //Testcase = Cin.Int;
            for (var _ = 0; _ < Testcase; _++) Solve();
        }
        static void Solve()
        {
            Cin.Scanf(out int N, out int Q);
            var Rfree = new HashSet<int>();
            var Rnum = new long[N+1];Fill(Rnum, -1);
            var Cfree = new HashSet<int>();
            var Cnum = new long[N+1];Fill(Cnum, -1);
            int rpre = N;
            int cpre = N;
            long ans = (long)(N - 2) * (N - 2);
            while (Q-- > 0)
            {
                Cin.Scanf(out int k, out int x);

                if (k == 1)//r
                {
                    if (x > rpre) { ans -= Rnum[x];continue; }
                    ans -= cpre - 2;
                    for(var i = rpre - 1; i >= x + 1; i--)
                    {
                        Rfree.Add(i);
                        Rnum[i] = cpre - 2;
                    }
                    rpre = x;
                }
                else
                {
                    if (x > cpre) { ans -= Cnum[x];continue; }
                    ans -= rpre - 2;
                    for(var i = cpre - 1; i >= x + 1; i--)
                    {
                        Cfree.Add(i);
                        Cnum[i] = rpre - 2;
                    }
                    cpre = x;
                }
            }
            OutL(ans);
        }
    }
    public struct Edge
    {
        public int from, to;
        public long w;
        public Edge(int to, long weight) { this.to = to; w = weight; from = -1; }
        public Edge(int from, int to, long weight) { this.from = from; this.to = to; w = weight; }
    }
    public class LCA
    {
        List<List<int>> G1;
        List<List<Edge>> G2;
        int n;
        bool isweighted;
        int[] dist;
        long[] dist_w;
        int[,] par;
        public LCA(List<List<int>> G)
        {
            G1 = G;
            G2 = null;
            n = G1.Count();
            isweighted = false;
            dist = new int[n];
            dist_w = null;
            par = new int[25, n];
        }
        public LCA(List<List<Edge>> G)
        {
            G1 = null;
            G2 = G;
            n = G2.Count();
            isweighted = true;
            dist = new int[n];
            dist_w = new long[n];
            par = new int[25, n];
        }

        public void Lca_Build(int root)
        {
            for (var i = 0; i < n; i++)
            {
                dist[i] = -1;
                if (isweighted) dist_w[i] = -1;
            }
            var dfs = new Stack<int>();
            dfs.Push(root);
            dist[root] = 0;
            if (isweighted) dist_w[root] = 0;
            par[0, root] = -1;
            while (dfs.Any())
            {
                int v = dfs.Pop();
                if (isweighted)
                {
                    foreach(var ed in G2[v])
                    {
                        if (dist[ed.to] != -1) continue;
                        par[0, ed.to] = v;
                        dist_w[ed.to] = dist[v] + ed.w;
                        dist[ed.to] = dist[v] + 1;
                        dfs.Push(ed.to);
                    }
                }
                else
                {
                    foreach(var nx in G1[v])
                    {
                        if (dist[nx] != -1) continue;
                        par[0, nx] = v;
                        dist[nx] = dist[v] + 1;
                        dfs.Push(nx);
                    }
                }
            }
            for(var i = 1; i < 25; i++)
            {
                for(var j = 0; j < n; j++)
                {
                    if (par[i - 1, j] == -1) par[i, j] = -1;
                    else par[i, j] = par[i - 1, par[i - 1, j]];
                }
            }
        }
        public int Lca(int u,int v)
        {
            if (dist[u] < dist[v])
            {
                var kep = u;
                u = v;
                v = kep;
            }
            for (var i = 0; i < 30; i++)
            {
                if ((((dist[u] - dist[v]) >> i) & 1) != 0)
                {
                    u = par[i, u];
                }
            }
            if (u == v) return u;
            for (var i = 24; i >= 0; i--)
            {
                if (par[i, u] != par[i, v])
                {
                    u = par[i, u];
                    v = par[i, v];
                }
            }
            return par[0, u];
        }
        public int[] GetDist() => dist;
        public long[] GetWeightedDist() => dist_w;
    }
    struct ModInt
    {
        public long value;
        //const int MOD = 1000000007;
        const int MOD = 998244353;
        public ModInt(long value) { this.value = value; }
        public override string ToString() => value.ToString();
        public static implicit operator ModInt(long a)
        {
            var ret = a % MOD;
            return new ModInt(ret < 0 ? (ret + MOD) : ret);
        }
        public static ModInt operator +(ModInt a, ModInt b) => (a.value + b.value);
        public static ModInt operator -(ModInt a, ModInt b) => (a.value - b.value);
        public static ModInt operator *(ModInt a, ModInt b) => (a.value * b.value);
        public static ModInt operator /(ModInt a, ModInt b) => a * Modpow(b, MOD - 2);

        public static ModInt operator <<(ModInt a, int n) => (a.value << n);
        public static ModInt operator >>(ModInt a, int n) => (a.value >> n);
        public static ModInt operator ++(ModInt a) => a.value + 1;
        public static ModInt operator --(ModInt a) => a.value - 1;
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static ModInt Modpow(ModInt a, long n)
        {
            if (n == 0) return 1;
            if (n < 0) return Modpow(Modpow(a, -n), MOD - 2);
            var k = a;
            ModInt ret = 1;
            while (n > 0)
            {
                if ((n & 1) != 0) ret *= k;
                k *= k;
                n >>= 1;
            }
            return ret;
        }
        private static readonly List<long> Factorials = new List<long>() { 1 };
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static ModInt Fac(int n)
        {
            if (n < 0) return 0;
            for (var i = Factorials.Count(); i <= n; i++)
            {
                Factorials.Add((Factorials[i - 1] * i) % MOD);
            }
            return Factorials[n];
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static ModInt nCr(int n, int r)
        {
            if (n < 0 || r < 0) return 0;
            return n < r ? 0 : Fac(n) / (Fac(r) * Fac(n - r));
        }
        public static explicit operator int(ModInt a) => (int)a.value;
    }
    public static class Graph
    {
        const long inf = long.MaxValue / 3;
        public static List<List<T>> Gen_Graph<T>(int size)
        {
            var ret = new List<List<T>>();
            for (var i = 0; i < size; i++) ret.Add(new List<T>());
            return ret;
        }
        public static long[] Dijkstra(List<List<Edge>> G, int st)
        {
            int N = G.Count();
            long[] ret = new long[N];
            var V = new Priority_Queue<Tuple<long, int>>((x, y) => Sig(x.Item1 - y.Item1));
            for (var i = 0; i < N; i++) ret[i] = inf;
            ret[st] = 0; V.Enqueue(new Tuple<long, int>(0, st));
            while (V.Any())
            {
                var cur = V.Dequeue();
                int v = cur.Item2;
                long cd = cur.Item1;
                if (ret[v] < cd) continue;
                foreach (var ed in G[v])
                {
                    if (ret[ed.to] > cd + ed.w)
                    {
                        ret[ed.to] = cd + ed.w;
                        V.Enqueue(new Tuple<long, int>(ret[ed.to], ed.to));
                    }
                }
            }
            return ret;
        }
        public static long[] Bellman_Frod(List<Edge> E, int st, int N, out bool neg_close)
        {
            var ret = new long[N];
            for (var i = 0; i < N; i++) ret[i] = inf;
            ret[st] = 0;
            for (var i = 0; i < N; i++)
            {
                foreach (var ed in E)
                {
                    if (ret[ed.from] != inf && ret[ed.to] > ret[ed.from] + ed.w)
                    {
                        if (i == N - 1) { neg_close = true; return ret; }
                        ret[ed.to] = ret[ed.from] + ed.w;
                    }
                }
            }
            neg_close = false;
            return ret;
        }
    }
    public class Priority_Queue<T>
    {
        private List<T> Q;
        private readonly Comparison<T> Func_Compare;
        public Priority_Queue(Comparison<T> comp)
        {
            Func_Compare = comp;
            Q = new List<T>();
        }
        private void PushHeap(T item)
        {
            int n = Q.Count();
            Q.Add(item);

            while (n != 0)
            {
                int pIndex = (n - 1) / 2;

                if (Func_Compare(Q[n], Q[pIndex]) < 0)
                {
                    Swap(n, pIndex);
                }
                else { break; }

                n = pIndex;
            }
        }
        private void PopHeap()
        {
            int n = Q.Count() - 1;
            Q[0] = Q[n];
            Q.RemoveAt(n);
            int cur = 0;
            int comp;
            while (2 * cur + 1 <= n - 1)
            {
                int c1 = 2 * cur + 1;
                int c2 = 2 * (cur + 1);
                if (c1 == n - 1)
                {
                    comp = c1;
                }
                else
                {

                    comp = Func_Compare(Q[c1], Q[c2]) < 0 ? c1 : c2;
                }

                if (Func_Compare(Q[cur], Q[comp]) > 0)
                {
                    Swap(cur, comp);
                }
                else { break; }

                cur = comp;
            }
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private void Swap(int a, int b)
        {
            T keep = Q[a];
            Q[a] = Q[b];
            Q[b] = keep;
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Enqueue(T value) => PushHeap(value);
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public T Dequeue()
        {
            T ret = Q[0];
            PopHeap();
            return ret;
        }
        public T Peek() => Q[0];
        public int Count() => Q.Count();
        public bool Any() => Q.Any();
    }
    public class SegmentTree<T>
    {
        //1-indexed type
        int n;
        T[] Tree;
        Func<T, T, T> f;
        T ex;
        int L;
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public SegmentTree(int size, Func<T, T, T> fun, T exvalue)
        {
            ex = exvalue;
            f = fun;
            n = size;
            Tree = new T[n << 1];
            L = (n << 1) - 1;
            for (var i = 0; i <= L; i++) Tree[i] = ex;
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public SegmentTree(int size, Func<T, T, T> fun, T exvalue, T[] initial)
        {
            ex = exvalue;
            n = size;
            f = fun;
            Tree = new T[n << 1];
            L = (n << 1) - 1;
            for (var i = 0; i <= L; i++) Tree[i] = (n <= i && i <= n + initial.Length - 1) ? initial[i - n] : ex;
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Set_All()
        {
            for (var i = n - 1; i >= 1; i--) Tree[i] = f(Tree[i << 1], Tree[(i << 1) | 1]);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Assign(int idx, T nxt) => Tree[idx + n] = nxt;
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Update(int idx)
        {
            int now = idx + n;
            while (now > 1)
            {
                now >>= 1;
                Tree[now] = f(Tree[now << 1], Tree[now << 1 | 1]);
            }
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Query_Update(int idx, T nxt)
        {
            Assign(idx, nxt); Update(idx);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Query_Update_func(int idx, T y)
        {
            Assign(idx, f(Peek(idx), y)); Update(idx);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public T Query_Fold(int l, int r)
        {
            int L = n + l;
            int R = n + r;
            T vL = ex, vR = ex;
            while (L < R)
            {
                if (L % 2 == 1)
                {
                    vL = f(vL, Tree[L]);
                    L++;
                }
                if (R % 2 == 1)
                {
                    vR = f(Tree[R - 1], vR);
                    R--;
                }
                L >>= 1;
                R >>= 1;
            }
            return f(vL, vR);
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public T Peek(int idx) => Tree[idx + n];
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void Display(int len)
        {
            for (var i = 0; i < len; i++) Console.Write($"{Tree[i + n]} ");
            Console.WriteLine();
        }
    }
    public class LazySegmentTree<X, A>
    {
        int n, L;
        X[] Tree;
        A[] lazy;
        Func<X, X, X> fxx;
        Func<A, A, A> faa;
        Func<X, A, X> fxa;
        X exx;
        A exa;
        public LazySegmentTree(int size, Func<X, X, X> funcxx, Func<A, A, A> funcaa, Func<X, A, X> funcxa, X exval, A exlaz)
        {
            n = size;
            L = (n << 1) - 1;
            Tree = new X[n << 1];
            lazy = new A[n << 1];
            fxx = funcxx;
            faa = funcaa;
            fxa = funcxa;
            exx = exval;
            exa = exlaz;
            for (var i = 0; i <= L; i++) { Tree[i] = exx; lazy[i] = exa; }
        }
        public X eval(int id) => fxa(Tree[id], lazy[id]);
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void propagate(int id)
        {
            int h = 0; while ((1 << (h + 1)) <= id) h++;
            for (var n = h; n > 0; n--)
            {
                int i = id >> n;
                Tree[i] = eval(i);
                lazy[i << 1] = faa(lazy[i << 1], lazy[i]);
                lazy[i << 1 | 1] = faa(lazy[i << 1 | 1], lazy[i]);
                lazy[i] = exa;
            }
        }
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public void re_calc(int id)
        {
            while (id > 1)
            {
                id >>= 1;
                Tree[id] = fxx(eval(id << 1), eval(id << 1 | 1));
            }
        }
        public void Range_Update(int l, int r, A op)
        {
            int L = n + l, R = n + r;
            int ll = L / (L & (-L));
            int rr = R / (R & (-R));
            propagate(ll); propagate(rr - 1);
            while (L < R)
            {
                if ((L & 1) == 1)
                {
                    lazy[L] = faa(lazy[L], op);
                    L++;
                }
                if ((R & 1) == 1)
                {
                    R--;
                    lazy[R] = faa(lazy[R], op);
                }
                L >>= 1; R >>= 1;
            }
            re_calc(ll); re_calc(rr - 1);
        }
        public X Range_Get(int l, int r)
        {
            int L = n + l, R = n + r;
            X vL = exx, vR = exx;
            propagate(L / (L & (-L)));
            propagate(R / (R & (-R)) - 1);
            while (L < R)
            {
                if ((L & 1) == 1)
                {
                    vL = fxx(vL, eval(L));
                    L++;
                }
                if ((R & 1) == 1)
                {
                    R--;
                    vR = fxx(eval(R), vR);
                }
                L >>= 1; R >>= 1;
            }
            return fxx(vL, vR);
        }
        public void Point_Update(int idx, X nxt)
        {
            int id = idx + n;
            propagate(id);
            Tree[id] = nxt;
            re_calc(id);
        }

        /*======================*/
        public void Assign(int idx, X nxt) => Tree[n + idx] = nxt;
        public void Set_All()
        {
            for (var i = n - 1; i >= 1; i--)
            {
                Tree[i] = fxx(Tree[i << 1], Tree[i << 1 | 1]);
                lazy[i] = faa(lazy[i << 1], lazy[i << 1 | 1]);
            }
        }
        public X Peek(int idx) => eval(idx);
        public void Display(int len)
        {
            for (var i = n; i < n + len; i++) Console.Write($"{eval(i)} ");
            Console.WriteLine();
        }
        public void Displayall()
        {
            //木の形で表示、nが2冪でない時は注意
            int e = 0;
            while ((1 << e) <= n)
            {
                for (var i = (1 << e); i < (1 << e) + (1 << e); i++) Console.Write($"{Tree[i]}/{lazy[i]} ");
                Console.WriteLine();
                e++;
            }
        }
    }
    public class UnionFind
    {
        private int[] parent;
        private int[] rank;
        private int[] size;
        public UnionFind(int n)
        {
            parent = new int[n];
            rank = new int[n];
            size = new int[n];
            for (var i = 0; i < n; i++)
            {
                parent[i] = i;
                rank[i] = 0;
                size[i] = 1;
            }
        }

        public int Root(int x)
        {
            return parent[x] == x ? x : parent[x] = Root(parent[x]);
        }

        public bool SameRoot(int x, int y)
        {
            return Root(x) == Root(y);
        }

        public void Unite(int x, int y)
        {
            x = Root(x);
            y = Root(y);
            if (x == y) { return; }

            if (rank[x] < rank[y])
            {
                parent[x] = y;
                size[y] += size[x];
                size[x] = 0;
            }
            else
            {
                parent[y] = x;
                if (rank[x] == rank[y]) { rank[x]++; }
                size[x] += size[y];
                size[y] = 0;
            }
        }

        public int SizeOf(int x)
        {
            return size[Root(x)];
        }

    }
    static class Cin
    {
        public static string[] ReadSplit => Console.ReadLine().Split();
        public static int[] ReadSplitInt => ConvertAll(ReadSplit, int.Parse);
        public static long[] ReadSplitLong => ConvertAll(ReadSplit, long.Parse);
        public static double[] ReadSplit_Double => ConvertAll(ReadSplit, double.Parse);
        public static string Str => Console.ReadLine();
        public static int Int => int.Parse(Console.ReadLine());
        public static long Long => long.Parse(Console.ReadLine());
        public static double Double => double.Parse(Console.ReadLine());
        public static T Conv<T>(string input)
        {
            if (typeof(T).Equals(typeof(ModInt)))
            {
                return (T)(dynamic)(long.Parse(input));
            }
            return (T)Convert.ChangeType(input, typeof(T));
        }
        public static void Scanf<T>(out T a) => a = Conv<T>(Console.ReadLine());
        public static void Scanf<T, U>(out T a, out U b)
        { var q = ReadSplit; a = Conv<T>(q[0]); b = Conv<U>(q[1]); }
        public static void Scanf<T, U, V>(out T a, out U b, out V c)
        { var q = ReadSplit; a = Conv<T>(q[0]); b = Conv<U>(q[1]); c = Conv<V>(q[2]); }
        public static void Scanf<T, U, V, W>(out T a, out U b, out V c, out W d)
        { var q = ReadSplit; a = Conv<T>(q[0]); b = Conv<U>(q[1]); c = Conv<V>(q[2]); d = Conv<W>(q[3]); }
        public static void Scanf<T, U, V, W, X>(out T a, out U b, out V c, out W d, out X e)
        { var q = ReadSplit; a = Conv<T>(q[0]); b = Conv<U>(q[1]); c = Conv<V>(q[2]); d = Conv<W>(q[3]); e = Conv<X>(q[4]); }
    }
    static class Cout
    {
        public static void OutL(object s) => Console.WriteLine(s);
        public static void Out_Sep<T>(IEnumerable<T> s) => Console.WriteLine(string.Join(" ", s));
        public static void Out_Sep<T>(IEnumerable<T> s, string sep) => Console.WriteLine(string.Join($"{sep}", s));
        public static void Out_Sep(params object[] s) => Console.WriteLine(string.Join(" ", s));
        public static void Out_One(object s) => Console.Write($"{s} ");
        public static void Out_One(object s, string sep) => Console.Write($"{s}{sep}");
        public static void Endl() => Console.WriteLine();
    }
    public static class Tool
    {
        static public void Initialize<T>(ref T[] array, T initialvalue)
        {
            array = ConvertAll(array, x => initialvalue);
        }
        static public void Swap<T>(ref T a, ref T b)
        {
            T keep = a;
            a = b;
            b = keep;
        }
        static public void Display<T>(T[,] array2d, int n, int m)
        {
            for (var i = 0; i < n; i++)
            {
                for (var j = 0; j < m; j++)
                {
                    Console.Write($"{array2d[i, j]} ");
                }
                Console.WriteLine();
            }
        }
        static public long Gcd(long a, long b)
        {
            if (a == 0 || b == 0) return Max(a, b);
            return a % b == 0 ? b : Gcd(b, a % b);
        }
        static public long LPow(int a, int b) => (long)Pow(a, b);
        static public bool Bit(long x, int dig) => ((1L << dig) & x) != 0;
        static public int Sig(long a) => a == 0 ? 0 : (int)(a / Abs(a));
    }
}