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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.InputMismatchException;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.TreeSet;

public class Main {
    void solve(MyScanner in, MyWriter out) {
        int n = in.nextInt();
        int q = in.nextInt();
        long ans = (long)(n - 2) * (n - 2);
        var hBIT = new RangeBinaryIndexedTree(n);
        var hSet = new TreeSet<Integer>();
        var wBIT = new RangeBinaryIndexedTree(n);
        var wSet = new TreeSet<Integer>();
        hBIT.addRange(n - 2, 2);
        wBIT.addRange(n - 2, 2);
        hSet.add(n);
        wSet.add(n);
        for (int i = 0; i < q; i++) {
            int _1or2 = in.nextInt();
            int x = in.nextInt();
            if (_1or2 == 1) {
                ans -= wBIT.get(x);
                int first = wSet.first();
                if (x < first) {
                    wSet.add(x);
                    hBIT.addRange(-(first - 2 - (x - 2)), 2, hSet.first());
                }
            } else {
                ans -= hBIT.get(x);
                int first = hSet.first();
                if (x < first) {
                    hSet.add(x);
                    wBIT.addRange(-(first - 2 - (x - 2)), 2, wSet.first());
                }
            }
        }
        out.println(ans);
    }
    static final class RangeBinaryIndexedTree {
        final int length;
        final BinaryIndexedTree tree;
        RangeBinaryIndexedTree(int length) {
            this.length = length;
            tree = new BinaryIndexedTree(length + 1);
        }
        void addRange(long value, int fromIndex) {
            addRange(value, fromIndex, length);
        }
        void addRange(long value, int fromIndex, int toIndex) {
            Objects.checkFromToIndex(fromIndex, toIndex, length);
            if (value == 0 || fromIndex == toIndex)
                return;
            tree.add(fromIndex, value);
            tree.add(toIndex, -value);
        }
        long get(int index) {
            return tree.prefixSum(index + 1);
        }
    }
    static final class BinaryIndexedTree {
        final int length;
        final long[] a;

        BinaryIndexedTree(int length) {
            if (length < 1) {
                throw new IllegalArgumentException();
            }
            this.length = length;
            this.a = new long[length + 1];
        }
        void add(int index, long value) {
            if (index < 0 || index >= length) {
                throw new IndexOutOfBoundsException();
            }
            for (int j = index + 1; j <= length; j += Integer.lowestOneBit(j)) {
                a[j] += value;
            }
        }
        long prefixSum(int toIndex) {
            if (toIndex < 0 || toIndex > length) {
                throw new IndexOutOfBoundsException();
            }
            long result = 0;
            for (int i = toIndex; i >= 1; i -= Integer.lowestOneBit(i)) {
                result += a[i];
            }
            return result;
        }
        long get(int index) {
            return prefixSum(index + 1) - prefixSum(index);
        }
        void set(int index, long value) {
            add(index, value - get(index));
        }
    }
    public static void main(String[] args) {
        MyWriter w = new MyWriter(System.out);
        new Main().solve(new MyScanner(System.in), w);
        w.flush();
    }
    static final class MyScanner {
        static final int BUFFER_SIZE = 8192;
        private final InputStream in;
        private final byte[] buffer = new byte[BUFFER_SIZE];
        private int point;
        private int readLength;

        MyScanner(InputStream in) {
            this.in = in;
        }
        private int readByte() {
            if (point < readLength) {
                int result = buffer[point];
                point += 1;
                return result;
            }
            try {
                readLength = in.read(buffer);
            } catch (IOException e) {
                throw new AssertionError(null, e);
            }
            if (readLength == -1) {
                return -1;
            }
            point = 1;
            return buffer[0];
        }
        private static boolean isVisibleChar(int c) {
            return 33 <= c && c <= 126;
        }
        char nextChar() {
            int c = readByte();
            while (!(c == -1 || isVisibleChar(c))) {
                c = readByte();
            }
            if (c == -1) {
                throw new NoSuchElementException();
            }
            return (char)c;
        }
        String next() {
            return next(16);
        }
        String next(int n) {
            int c = readByte();
            while (!(c == -1 || isVisibleChar(c))) {
                c = readByte();
            }
            if (c == -1) {
                throw new NoSuchElementException();
            }
            StringBuilder b = new StringBuilder(n);
            do {
                b.append((char)c);
                c = readByte();
            } while (c != -1 && isVisibleChar(c));
            return b.toString();
        }
        long nextLong() {
            int c = readByte();
            while (!(c == -1 || isVisibleChar(c))) {
                c = readByte();
            }
            if (c == -1) {
                throw new NoSuchElementException();
            }
            boolean minus = false;
            long limit = -Long.MAX_VALUE;
            if (c == '-') {
                minus = true;
                limit = Long.MIN_VALUE;
                c = readByte();
            }
            long n = 0L;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                if (n < limit / 10L) {
                    throw new InputMismatchException();
                }
                n *= 10L;
                int digit = c - '0';
                if (n < limit + digit) {
                    throw new InputMismatchException();
                }
                n -= digit;
                c = readByte();
            } while (c != -1 && isVisibleChar(c));
            return minus ? n : -n;
        }
        int nextInt() {
            long n = nextLong();
            if (n < Integer.MIN_VALUE || n > Integer.MAX_VALUE) {
                throw new InputMismatchException();
            }
            return (int)n;
        }
        double nextDouble() {
            return Double.parseDouble(next());
        }
        int[] nextIntArray(int n) {
            int[] result = new int[n];
            for (int i = 0; i < n; i++) {
                result[i] = nextInt();
            }
            return result;
        }
        long[] nextLongArray(int n) {
            long[] result = new long[n];
            for (int i = 0; i < n; i++) {
                result[i] = nextLong();
            }
            return result;
        }
        char[] nextCharArray(int n) {
            char[] result = new char[n];
            for (int i = 0; i < n; i++) {
                result[i] = nextChar();
            }
            return result;
        }
        char[][] next2dCharArray(int h, int w) {
            char[][] result = new char[h][w];
            for (int i = 0; i < h; i++) {
                for (int j = 0; j < w; j++) {
                    result[i][j] = nextChar();
                }
            }
            return result;
        }
        int[][] nextVerticalIntArrays(int arrayCount, int arrayLength) {
            int[][] result = new int[arrayCount][arrayLength];
            for (int i = 0; i < arrayLength; i++) {
                for (int j = 0; j < arrayCount; j++) {
                    result[j][i] = nextInt();
                }
            }
            return result;
        }
        long[][] nextVerticalLongArrays(int arrayCount, int arrayLength) {
            long[][] result = new long[arrayCount][arrayLength];
            for (int i = 0; i < arrayLength; i++) {
                for (int j = 0; j < arrayCount; j++) {
                    result[j][i] = nextLong();
                }
            }
            return result;
        }
        char[][] nextVerticalCharArrays(int arrayCount, int arrayLength) {
            char[][] result = new char[arrayCount][arrayLength];
            for (int i = 0; i < arrayLength; i++) {
                for (int j = 0; j < arrayCount; j++) {
                    result[j][i] = nextChar();
                }
            }
            return result;
        }
        List<String> nextStringList(int n) {
            var result = new ArrayList<String>(n);
            for (int i = 0; i < n; i++) {
                result.add(next());
            }
            return result;
        }
        List<Integer> nextIntList(int n) {
            var result = new ArrayList<Integer>(n);
            for (int i = 0; i < n; i++) {
                result.add(nextInt());
            }
            return result;
        }
        List<Long> nextLongList(int n) {
            var result = new ArrayList<Long>(n);
            for (int i = 0; i < n; i++) {
                result.add(nextLong());
            }
            return result;
        }
    }
    static final class MyWriter extends PrintWriter {
        MyWriter(OutputStream out) {
            super(out);
        }
        void println(int[] x) {
            println(x, " ");
        }
        void println(int[] x, String delimiter) {
            if (x.length > 0) {
                print(x[0]);
                for (int i = 1; i < x.length; i++) {
                    print(delimiter);
                    print(x[i]);
                }
            }
            println();
        }
        void println(long[] x) {
            println(x, " ");
        }
        void println(long[] x, String delimiter) {
            if (x.length > 0) {
                print(x[0]);
                for (int i = 1; i < x.length; i++) {
                    print(delimiter);
                    print(x[i]);
                }
            }
            println();
        }
        void println(Iterable<?> iterable) {
            println(iterable, " ");
        }
        void println(Iterable<?> iterable, String delimiter) {
            Iterator<?> i = iterable.iterator();
            if (i.hasNext()) {
                print(i.next());
                while (i.hasNext()) {
                    print(delimiter);
                    print(i.next());
                }
            }
            println();
        }
        void printLines(int[] x) {
            println(x, System.lineSeparator());
        }
        void printLines(long[] x) {
            println(x, System.lineSeparator());
        }
        void printLines(Iterable<?> iterable) {
            println(iterable, System.lineSeparator());
        }
    }
}