#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
#pragma warning (disable: 4996)
class SegmentTree {
public:
vector<long long> dat1, dat2; int size_ = 1;
void init(int sz) {
while (size_ <= sz) size_ *= 2;
dat1.resize(size_ * 2, 0);
dat2.resize(size_ * 2, 0);
}
void add(int pos,long long x) {
pos += size_;
while (pos >= 1) {
dat1[pos]++; dat2[pos] += x;
pos >>= 1;
}
}
void lose(int pos, long long x) {
pos += size_;
while (pos >= 1) {
dat1[pos]--; dat2[pos] -= x;
pos >>= 1;
}
}
long long getmax(long long M) {
int u = 1; long long cx = 0;
while (u < size_) {
if (dat1[u * 2 + 1] <= M) {
M -= dat1[u * 2 + 1];
cx += dat2[u * 2 + 1];
u = u * 2;
}
else {
u = u * 2 + 1;
}
}
if (M > 0) {
M -= dat1[u];
cx += dat2[u];
if (M > 0) return -(1LL << 60);
}
return cx;
}
};
long long N, M, C[1 << 18], V[1 << 18], ans[1 << 18], id[1 << 18], SIZE_ = 1;
vector<pair<long long, long long>>A, B;
int main() {
// --------------------------- 入力・ソート ----------------------
scanf("%lld%lld", &N, &M);
for (int i = 0; i < N; i++) {
scanf("%lld%lld", &V[i], &C[i]);
A.push_back(make_pair(C[i], V[i]));
}
sort(A.begin(), A.end());
for (int i = 1; i <= N; i++) {
C[i] = A[i - 1].first; V[i] = A[i - 1].second;
B.push_back(make_pair(V[i], i));
}
sort(B.begin(), B.end());
// ---------------------------- ただの分割 -----------------------
while (SIZE_ <= N) SIZE_ *= 2;
ans[SIZE_] = -(1LL << 60); id[SIZE_] = N;
ans[0] = -(1LL << 60); id[0] = 1;
for (int i = (SIZE_ >> 1); i >= 1; i >>= 1) {
vector<int> vec;
for (int j = i; j < SIZE_; j += i * 2) vec.push_back(j);
SegmentTree Z; Z.init(SIZE_ + 1);
int cx = N + 1;
for (int j = vec.size() - 1; j >= 0; j--) {
// 新たに追加する
for (int k = vec[j]; k < min((int)id[vec[j] + i] + 1, cx); k++) {
if (k <= N) {
int pos1 = lower_bound(B.begin(), B.end(), make_pair(V[k], 1LL * k)) - B.begin();
Z.add(pos1, V[k]);
}
}
// 答えを求める
pair<long long, int> maxid = make_pair(-(1LL << 59), N);
for (int k = id[vec[j] + i]; k >= id[vec[j] - i]; k--) {
long long v = Z.getmax(M) - 2LL * (C[k] - C[vec[j]]);
maxid = max(maxid, make_pair(v, k));
if (k >= vec[j] && k != id[vec[j] - i]) {
int pos1 = lower_bound(B.begin(), B.end(), make_pair(V[k], 1LL * k)) - B.begin();
Z.lose(pos1, V[k]);
}
}
ans[vec[j]] = maxid.first;
id[vec[j]] = maxid.second;
cx = vec[j];
}
}
// --------------------------- 答えを求める ----------------------
long long FinalAns = -(1LL << 60);
for (int i = 1; i <= N; i++) FinalAns = max(FinalAns, ans[i]);
cout << FinalAns << endl;
return 0;
}
