package contest231124;
import java.io.*;
import java.util.*;
import java.util.function.IntUnaryOperator;
import java.util.function.LongUnaryOperator;

public class F2 {
	InputStream is;
	FastWriter out;

	String INPUT = "";

	public void solve()
	{
		// maximize
		// f(X) = sum_{i=1}^n (a_i * X_i + d_i * X_i * (X_i-1)/2
		// sum x_i = m

		// 増加列は1つだけ選べば良い？

		int n = ni(), m = ni();
		int[][] ad = nmi(n, 2);

		List<int[]> asc = new ArrayList<>();
		PriorityQueue<long[]> pq = new PriorityQueue<>((x, y) -> Long.compare(y[0], x[0]));
		for(int i = 0;i < n;i++){
			if(ad[i][1] > 0){
				asc.add(ad[i]);
			}else{
				pq.add(new long[]{ad[i][0], ad[i][1]});
			}
		}

		if(pq.isEmpty()){
			long ans = Long.MIN_VALUE;
			for(int[] u : asc){
				ans = Math.max(ans, (long)u[0]*m + u[1]*(long)m*(m-1)/2);
			}
			out.println(ans);
			return;
		}

		long[] maxs = new long[m+1];
		for(int i = 0;i < m;i++){
			long[] v = pq.poll();
			maxs[i+1] = maxs[i] + v[0];
			v[0] += v[1];
			pq.add(v);
		}

		// -(a+(m-t)d) + bm[t]

		if(asc.size() == 0){
			out.println(maxs[m]);
			return;
		}

		LiChaoTree lct = new LiChaoTree(0, 20);
		// u[0]*x + u[1]*x*(x-1)/2
		// u[0] + u[1]*(x-1)/2
		for(int[] u : asc){
			lct.add(-u[1], u[1]-2L*u[0]);
		}
		long ans = Long.MIN_VALUE;
		for(int i = 0;i <= m;i++){
			ans = Math.max(ans, maxs[m-i] - lct.f(i) * i / 2);
		}
		out.println(ans);
	}

	public static class LiChaoTree {
		public LL as;
		public LL bs;

		public long L;
		public int D;
		public L lefts, rights;

		// [L, L+(1<<D))
		public LiChaoTree(long L, int D)
		{
			as = new LL(2);
			bs = new LL(2);
			lefts = new L(2);
			rights = new L(2);
			this.L = L;
			this.D = D;
			as.add(0L);
			bs.add(Long.MAX_VALUE);
			lefts.add(-1);
			rights.add(-1);
		}

		public static long f(long x, long a, long b)
		{
			return a*x+b;
		}

		public void add(long a, long b) { add(a, b, L, L+(1L<<D)); }

		public void add(long a, long b, long l, long r) {
			add(a, b, 0, l, r, L, L+(1L<<D));
		}

		public int add(long a, long b, int cur, long l, long r, long cl, long cr) {
			// [l,r)
			if(cl >= cr)return -1;
			if(l <= cl && cr <= r){
				if(cur == -1){
					as.add(a);
					bs.add(b);
					lefts.add(-1);
					rights.add(-1);
					return as.p-1;
				}
				boolean lessl = f(cl, a, b) < f(cl, as.a[cur], bs.a[cur]);
				boolean lessr = f(cr-1, a, b) < f(cr-1, as.a[cur], bs.a[cur]);
				if(!lessl && !lessr){
					// not need to append
					return cur;
				}
				if(lessl && lessr){
					// replace current
					as.a[cur] = a; bs.a[cur] = b; return cur;
				}
				long cm = cl + (cr-cl)/2;
				boolean lessm = f(cm, a, b) < f(cm, as.a[cur], bs.a[cur]);
				if(lessm){
					{long d = as.a[cur]; as.a[cur] = a; a = d;}
					{long d = bs.a[cur]; bs.a[cur] = b; b = d;}
					lessl = !lessl;
					lessr = !lessr;
				}
				if(lessl){
					int res = add(a, b, lefts.a[cur], l, r, cl, cm);
					lefts.a[cur] = res;
				}else{
					int res = add(a, b, rights.a[cur], l, r, cm, cr);
					rights.a[cur] = res;
				}
				return cur;
			}

			long cm = cl + (cr-cl)/2;
			if(cur == -1){
				as.add(0);
				bs.add(Long.MAX_VALUE);
				lefts.add(-1);
				rights.add(-1);
				cur = as.p-1;
			}
			if(l < cm){
				int res = add(a, b, lefts.a[cur], l, r, cl, cm);
				lefts.a[cur] = res;
			}
			if(cm < r){
				int res = add(a, b, rights.a[cur], l, r, cm, cr);
				rights.a[cur] = res;
			}
			return cur;
		}

		public long f(long x)
		{
			assert L <= x;
			assert x < L+(1L<<D);
			int cur = 0;
			long min = Long.MAX_VALUE;
			for(long m = D;m >= 0 && cur != -1;m--){
				min = Math.min(min, f(x, as.a[cur], bs.a[cur]));
				cur = x-L<< -m <0 ? rights.a[cur] : lefts.a[cur];
			}
			return min;
		}

		public static class L {
			public int[] a;
			public int p = 0;

			public L(int n) { a = new int[n]; }
			public L add(int n)
			{
				if(p >= a.length)a = Arrays.copyOf(a, a.length*3/2+1);
				a[p++] = n;
				return this;
			}
			public int size() { return p; }
			public L clear() { p = 0; return this; }
			public int[] toArray() { return Arrays.copyOf(a, p); }
			@Override
			public String toString() {return Arrays.toString(toArray());}
		}

		public static class LL {
			public long[] a;
			public int p = 0;

			public LL(int n) { a = new long[n]; }
			public LL add(long n)
			{
				if(p >= a.length)a = Arrays.copyOf(a, a.length*3/2+1);
				a[p++] = n;
				return this;
			}
			public int size() { return p; }
			public LL clear() { p = 0; return this; }
			public long[] toArray() { return Arrays.copyOf(a, p); }
			@Override
			public String toString() {return Arrays.toString(toArray());}
		}
	}


	public static void main(String[] args) {
		new F2().run();
	}

	public void run()
	{
		long S = System.currentTimeMillis();
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new FastWriter(System.out);

		solve();
		out.flush();
		long G = System.currentTimeMillis();
		tr(G-S+"ms");
		//		Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){
		//			@Override
		//			public void run() {
		//				long s = System.currentTimeMillis();
		//				solve();
		//				out.flush();
		//				if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
		//			}
		//		};
		//		t.start();
		//		t.join();
	}

	private boolean eof()
	{
		if(lenbuf == -1)return true;
		int lptr = ptrbuf;
		while(lptr < lenbuf)if(!isSpaceChar(inbuf[lptr++]))return false;

		try {
			is.mark(1000);
			while(true){
				int b = is.read();
				if(b == -1){
					is.reset();
					return true;
				}else if(!isSpaceChar(b)){
					is.reset();
					return false;
				}
			}
		} catch (IOException e) {
			return true;
		}
	}

	private final byte[] inbuf = new byte[1024];
	public int lenbuf = 0, ptrbuf = 0;

	private int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}

	private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
	//	private boolean isSpaceChar(int c) { return !(c >= 32 && c <= 126); }
	private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }

	private double nd() { return Double.parseDouble(ns()); }
	private char nc() { return (char)skip(); }

	private String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	private char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}

	private char[][] nm(int n, int m)
	{
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}

	private int[][] nmi(int n, int m)
	{
		int[][] map = new int[n][];
		for(int i = 0;i < n;i++)map[i] = na(m);
		return map;
	}

	private int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}

	private long[] nal(int n)
	{
		long[] a = new long[n];
		for(int i = 0;i < n;i++)a[i] = nl();
		return a;
	}

	private int ni()
	{
		int num = 0, b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}

		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}

	private long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}

		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}

	public static class FastWriter
	{
		private static final int BUF_SIZE = 1<<13;
		private final byte[] buf = new byte[BUF_SIZE];
		private final OutputStream out;
		private int ptr = 0;

		private FastWriter(){out = null;}

		public FastWriter(OutputStream os)
		{
			this.out = os;
		}

		public FastWriter(String path)
		{
			try {
				this.out = new FileOutputStream(path);
			} catch (FileNotFoundException e) {
				throw new RuntimeException("FastWriter");
			}
		}

		public FastWriter write(byte b)
		{
			buf[ptr++] = b;
			if(ptr == BUF_SIZE)innerflush();
			return this;
		}

		public FastWriter write(char c)
		{
			return write((byte)c);
		}

		public FastWriter write(char[] s)
		{
			for(char c : s){
				buf[ptr++] = (byte)c;
				if(ptr == BUF_SIZE)innerflush();
			}
			return this;
		}

		public FastWriter write(String s)
		{
			s.chars().forEach(c -> {
				buf[ptr++] = (byte)c;
				if(ptr == BUF_SIZE)innerflush();
			});
			return this;
		}

		private static int countDigits(int l) {
			if (l >= 1000000000) return 10;
			if (l >= 100000000) return 9;
			if (l >= 10000000) return 8;
			if (l >= 1000000) return 7;
			if (l >= 100000) return 6;
			if (l >= 10000) return 5;
			if (l >= 1000) return 4;
			if (l >= 100) return 3;
			if (l >= 10) return 2;
			return 1;
		}

		public FastWriter write(int x)
		{
			if(x == Integer.MIN_VALUE){
				return write((long)x);
			}
			if(ptr + 12 >= BUF_SIZE)innerflush();
			if(x < 0){
				write((byte)'-');
				x = -x;
			}
			int d = countDigits(x);
			for(int i = ptr + d - 1;i >= ptr;i--){
				buf[i] = (byte)('0'+x%10);
				x /= 10;
			}
			ptr += d;
			return this;
		}

		private static int countDigits(long l) {
			if (l >= 1000000000000000000L) return 19;
			if (l >= 100000000000000000L) return 18;
			if (l >= 10000000000000000L) return 17;
			if (l >= 1000000000000000L) return 16;
			if (l >= 100000000000000L) return 15;
			if (l >= 10000000000000L) return 14;
			if (l >= 1000000000000L) return 13;
			if (l >= 100000000000L) return 12;
			if (l >= 10000000000L) return 11;
			if (l >= 1000000000L) return 10;
			if (l >= 100000000L) return 9;
			if (l >= 10000000L) return 8;
			if (l >= 1000000L) return 7;
			if (l >= 100000L) return 6;
			if (l >= 10000L) return 5;
			if (l >= 1000L) return 4;
			if (l >= 100L) return 3;
			if (l >= 10L) return 2;
			return 1;
		}

		public FastWriter write(long x)
		{
			if(x == Long.MIN_VALUE){
				return write("" + x);
			}
			if(ptr + 21 >= BUF_SIZE)innerflush();
			if(x < 0){
				write((byte)'-');
				x = -x;
			}
			int d = countDigits(x);
			for(int i = ptr + d - 1;i >= ptr;i--){
				buf[i] = (byte)('0'+x%10);
				x /= 10;
			}
			ptr += d;
			return this;
		}

		public FastWriter write(double x, int precision)
		{
			if(x < 0){
				write('-');
				x = -x;
			}
			x += Math.pow(10, -precision)/2;
			//		if(x < 0){ x = 0; }
			write((long)x).write(".");
			x -= (long)x;
			for(int i = 0;i < precision;i++){
				x *= 10;
				write((char)('0'+(int)x));
				x -= (int)x;
			}
			return this;
		}

		public FastWriter writeln(char c){ return write(c).writeln(); }
		public FastWriter writeln(int x){ return write(x).writeln(); }
		public FastWriter writeln(long x){ return write(x).writeln(); }
		public FastWriter writeln(double x, int precision){ return write(x, precision).writeln(); }

		public FastWriter write(int... xs)
		{
			boolean first = true;
			for(int x : xs) {
				if (!first) write(' ');
				first = false;
				write(x);
			}
			return this;
		}

		public FastWriter write(long... xs)
		{
			boolean first = true;
			for(long x : xs) {
				if (!first) write(' ');
				first = false;
				write(x);
			}
			return this;
		}

		public FastWriter write(IntUnaryOperator f, int... xs)
		{
			boolean first = true;
			for(int x : xs) {
				if (!first) write(' ');
				first = false;
				write(f.applyAsInt(x));
			}
			return this;
		}

		public FastWriter write(LongUnaryOperator f, long... xs)
		{
			boolean first = true;
			for(long x : xs) {
				if (!first) write(' ');
				first = false;
				write(f.applyAsLong(x));
			}
			return this;
		}

		public FastWriter writeln()
		{
			return write((byte)'\n');
		}

		public FastWriter writeln(int... xs) { return write(xs).writeln(); }
		public FastWriter writeln(long... xs) { return write(xs).writeln(); }
		public FastWriter writeln(IntUnaryOperator f, int... xs) { return write(f, xs).writeln(); }
		public FastWriter writeln(LongUnaryOperator f, long... xs) { return write(f, xs).writeln(); }
		public FastWriter writeln(char[] line) { return write(line).writeln(); }
		public FastWriter writeln(char[]... map) { for(char[] line : map)write(line).writeln();return this; }
		public FastWriter writeln(String s) { return write(s).writeln(); }

		private void innerflush()
		{
			try {
				out.write(buf, 0, ptr);
				ptr = 0;
			} catch (IOException e) {
				throw new RuntimeException("innerflush");
			}
		}

		public void flush()
		{
			innerflush();
			try {
				out.flush();
			} catch (IOException e) {
				throw new RuntimeException("flush");
			}
		}

		public FastWriter print(byte b) { return write(b); }
		public FastWriter print(char c) { return write(c); }
		public FastWriter print(char[] s) { return write(s); }
		public FastWriter print(String s) { return write(s); }
		public FastWriter print(int x) { return write(x); }
		public FastWriter print(long x) { return write(x); }
		public FastWriter print(double x, int precision) { return write(x, precision); }
		public FastWriter println(char c){ return writeln(c); }
		public FastWriter println(int x){ return writeln(x); }
		public FastWriter println(long x){ return writeln(x); }
		public FastWriter println(double x, int precision){ return writeln(x, precision); }
		public FastWriter print(int... xs) { return write(xs); }
		public FastWriter print(long... xs) { return write(xs); }
		public FastWriter print(IntUnaryOperator f, int... xs) { return write(f, xs); }
		public FastWriter print(LongUnaryOperator f, long... xs) { return write(f, xs); }
		public FastWriter println(int... xs) { return writeln(xs); }
		public FastWriter println(long... xs) { return writeln(xs); }
		public FastWriter println(IntUnaryOperator f, int... xs) { return writeln(f, xs); }
		public FastWriter println(LongUnaryOperator f, long... xs) { return writeln(f, xs); }
		public FastWriter println(char[] line) { return writeln(line); }
		public FastWriter println(char[]... map) { return writeln(map); }
		public FastWriter println(String s) { return writeln(s); }
		public FastWriter println() { return writeln(); }
	}

	public static void trnz(int... o)
	{
		for(int i = 0;i < o.length;i++)if(o[i] != 0)System.out.print(i+":"+o[i]+" ");
		System.out.println();
	}

	// print ids which are 1
	public static void trt(long... o)
	{
		Queue<Integer> stands = new ArrayDeque<>();
		for(int i = 0;i < o.length;i++){
			for(long x = o[i];x != 0;x &= x-1)stands.add(i<<6|Long.numberOfTrailingZeros(x));
		}
		System.out.println(stands);
	}

	public static void tf(boolean... r)
	{
		for(boolean x : r)System.out.print(x?'#':'.');
		System.out.println();
	}

	public static void tf(boolean[]... b)
	{
		for(boolean[] r : b) {
			for(boolean x : r)System.out.print(x?'#':'.');
			System.out.println();
		}
		System.out.println();
	}

	public void tf(long[]... b)
	{
		if(INPUT.length() != 0) {
			for (long[] r : b) {
				for (long x : r) {
					for (int i = 0; i < 64; i++) {
						System.out.print(x << ~i < 0 ? '#' : '.');
					}
				}
				System.out.println();
			}
			System.out.println();
		}
	}

	public void tf(long... b)
	{
		if(INPUT.length() != 0) {
			for (long x : b) {
				for (int i = 0; i < 64; i++) {
					System.out.print(x << ~i < 0 ? '#' : '.');
				}
			}
			System.out.println();
		}
	}

	private void tr(Object... o) { if(INPUT.length() != 0)System.out.println(Arrays.deepToString(o)); }
}