#pragma comment(linker, "/STACK:1024000000,1024000000")

#include <cstdio>

#include <string>

#include <cstdlib>

#include <cmath>

#include <iostream>

#include <cstring>

#include <set>

#include <queue>

#include <algorithm>

#include <vector>

#include <map>

#include <cctype>

#include <cmath>

#include <stack>

#include <sstream>

#include <list>

#include <assert.h>

#include <bitset>

#define debug() puts("++++");

#define gcd(a, b) __gcd(a, b)

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define fi first

#define se second

#define pb push_back

#define sqr(x) ((x)*(x))

#define ms(a,b) memset(a, b, sizeof a)

//#define sz size()

#define pu push_up

#define pd push_down

#define cl clear()

#define FOR(x,n)  for(int i = (x); i < (n); ++i)

#define freopenr freopen("in.txt", "r", stdin)

#define freopenw freopen("out.txt", "w", stdout)

#define pii pair<int, int>

using namespace std;

typedef long long LL;

typedef unsigned long long ULL;

typedef pair<LL, int> P;

const int INF = 0x3f3f3f3f;

const LL LNF = 1e18;

const double inf = 1e20;

const double PI = acos(-1.0);

const double eps = 1e-8;

const int maxn = 1000 + 10;

const LL mod = 1e9 + 7;

const int dr[] = {-1, 0, 1, 0};

const int dc[] = {0, 1, 0, -1};

const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};

int n, m;

const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

inline bool is_in(int r, int c) {

  return r >= 0 && r < n && c >= 0 && c < m;

}

struct Node{

  int pos;

  LL val;

  Node(int p = 0, LL v = 0) : pos(p), val(v) { }

  bool operator < (const Node rhs) const{

    return pos > rhs.pos;

  }

};

Node node1[maxn], node2[maxn];

int main(){

  scanf("%d %d", &n, &m);

  int cnt1 = 0, cnt2 = 0;

  for(int i = 0; i < n; ++i){

    int a, b;  scanf("%d %d", &a, &b);

    if (a < 0)  node1[cnt1++] = Node(-a, b);

    else  node2[cnt2++] = Node(a, b);

  }

  sort(node1, node1 + cnt1);

  sort(node2, node2 + cnt2);

  LL ans = 0;

  LL pre_left = 0;

  for(int i = 0; i < cnt1; ++i){

    if (pre_left >= node1[i].val){

      pre_left -= node1[i].val;

      node1[i].val = 0;

      continue;

    }

    node1[i].val -= pre_left;

    LL num = (node1[i].val - 1) / m + 1;

    ans += num * node1[i].pos * 2;

    pre_left = num * m - node1[i].val;

  }

  pre_left = 0;

  for (int i = 0; i < cnt2; ++i){

    if (pre_left >= node2[i].val){

      pre_left -= node2[i].val;

      node2[i].val = 0;

      continue;

    }

    node2[i].val -= pre_left;

    LL num = (node2[i].val - 1) / m + 1;

    ans += num * node2[i].pos * 2;

    pre_left = num * m - node2[i].val;

  }

  printf("%I64d\n", ans);

  return 0;

}