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#!/usr/bin/env python3

import sys
from dataclasses import dataclass


def main():
    N, C = [int(x) for x in input().split()]
    blocks = []
    all_w = {}
    for i in range(N):
        row = [int(x) for x in input().split()]
        blocks.append(row)
        all_w[row[1]] = True
    blocks.sort(reverse=True)
    blocks_count = len(blocks)
    w_count = len(all_w)

    result = 0

    @dataclass
    class Ctx:
        score: int
        curr_a: int
        curr_w: int

    def f(at, ctx):
        nonlocal result
        if result < ctx.score:
            result = ctx.score
        used_w = {}
        for i in range(at, blocks_count):
            a, w = blocks[i]
            if ctx.curr_a != a and w not in used_w:
                used_w[w] = True
                score = ctx.score + a
                if ctx.curr_w != w and ctx.curr_w != -1:
                    score -= C
                f(i + 1, Ctx(score, a, w))
            if len(used_w) == w_count:
                break

    f(0, Ctx(0, -1, -1))
    print(result)


if __name__ == "__main__":
    if len(sys.argv) == 2:
        sys.stdin = open(sys.argv[1])
    main()