#ifdef LOCAL111
	#define _GLIBCXX_DEBUG
#else
	#define NDEBUG
#endif
#define _USE_MATH_DEFINES
#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <type_traits>
#include <typeindex>
#include <unordered_map>
#include <unordered_set>
#endif
const int INF = 1e9;
using namespace std;
template<typename T, typename U> ostream& operator<< (ostream& os, const pair<T,U>& p) { os << '(' << p.first << ' ' << p.second << ')'; return os; }

#define endl '\n'
#define ALL(a)  (a).begin(),(a).end()
#define SZ(a) int((a).size())
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n)  FOR(i,0,n)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#ifdef LOCAL111
	#define DEBUG(x) cout<<#x<<": "<<(x)<<endl
	template<typename T> void dpite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
#else
	#define DEBUG(x) true
	template<typename T> void dpite(T a, T b){ return; }
#endif
#define F first
#define S second
#define SNP string::npos
#define WRC(hoge) cout << "Case #" << (hoge)+1 << ": "
template<typename T> void pite(T a, T b){ for(T ite = a; ite != b; ite++) cout << (ite == a ? "" : " ") << *ite; cout << endl;}
template<typename T> bool chmax(T& a, T b){if(a < b){a = b; return true;} return false;}
template<typename T> bool chmin(T& a, T b){if(a > b){a = b; return true;} return false;}

typedef long long int LL;
typedef unsigned long long ULL;
typedef pair<int,int> P;

void ios_init(){
	//cout.setf(ios::fixed);
	//cout.precision(12);
#ifdef LOCAL111
	return;
#endif
	ios::sync_with_stdio(false); cin.tie(0);
}

int main()
{
	ios_init();
	int n;
	LL c;
	while(cin >> n >> c) {
		using P = pair<LL, LL>;
		vector<P> xv(n);
		REP(i, n) cin >> xv[i].F >> xv[i].S;
		sort(ALL(xv));
		LL ans = 0;
		{
			LL t = 0;
			REP(i, n) {
				t += xv[i].S;
			}
			sort(ALL(xv));
			chmax(ans, max(t-(c-xv[0].F), t-(xv[n-1].F)));
		}
		auto f = [&](){
			vector<LL> lma(n);
			vector<LL> rma(n);
			auto t = xv;
			sort(ALL(t));
			{
				LL sum = 0;
				REP(i, n) {
					sum += t[i].S;
					lma[i] = sum-2*t[i].F;
				}
			}
			chmax(lma[0], 0ll);
			REP(i, n-1) {
				chmax(lma[i+1], lma[i]);
			}
			REP(i, n) {
				t[i].F = c-t[i].F;
			}
			sort(ALL(t));
			{
				LL sum = 0;
				REP(i, n) {
					sum += t[i].S;
					rma[i] = sum-t[i].F;
				}
			}
			dpite(ALL(lma));
			dpite(ALL(rma));
			chmax(rma[0], 0ll);
			REP(i, n-1) {
				chmax(rma[i+1], rma[i]);
			}
			FOR(i, 0, n-1) {
				DEBUG(i); DEBUG(n-1-i-1);
				chmax(ans, lma[i] + rma[n-1-i-1]);
			}
			chmax(ans, rma[n-1]);



			// LL la = 0;
			// LL cs = 0;
			// int u = 0;
			// REP(i, n) {
			// 	cs += xv[i].S;
			// 	if(chmax(la, cs-xv[i].F)) {
			// 		u = n-i-1;
			// 	}
			// }

			// DEBUG(u);

			// dpite(ALL(xv));

			// auto t = xv;

			// chmax(ans, la);
			// cs = 0;

			// DEBUG(la);
			// REP(i, u) {
			// 	DEBUG(cs);
			// 	DEBUG(la + cs-t[i].F*2);
			// 	chmax(ans, la+cs-t[i].F*2);
			// }
			// DEBUG(ans);
		};

		f();
		REP(i, n) {
			xv[i].F = c-xv[i].F;
		}
		sort(ALL(xv));
		f();
		
		cout << ans << endl;
	}
	return 0;
}


Measured memory_bytes: 4992