Baekjoon #18234

import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) {
        FastReader rd = new FastReader();
        int N = rd.nextInt();
        int T = rd.nextInt();
        int a[][] = new int[N][2];

        for (int i = 0; i < N; i++) {
            a[i][0] = rd.nextInt();
            a[i][1] = rd.nextInt();
        }

        Arrays.sort(a, (n1, n2) -> {
            if (n1[1] == n2[1]) return n2[0] - n1[0];
            return n2[1] - n1[1];
        });

        int day = 1;
        long sum = 0;
        for (int i = 0; i < N; i++) {
            sum += 1L * a[i][1] * (T - day++) + a[i][0];
        }
        System.out.println(sum);
    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}