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#include<bits/stdc++.h>
using namespace std;
using LL=long long;
#define FOR(i,l,r)for(int i=(l);i<=(r);++i)
#define REP(i,n)FOR(i,0,(n)-1)
#define ssize(x)int(x.size())
#ifdef DEBUG
auto operator<<(auto&o,auto x)->decltype(x.end(),o);
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto&operator<<(auto&o,tuple<auto,auto,auto>t){return o<<"("<<get<0>(t)<<", "<<get<1>(t)<<", "<<get<2>(t)<<")";}
auto&operator<<(auto&o,tuple<auto,auto,auto,auto>t){return o<<"("<<get<0>(t)<<", "<<get<1>(t)<<", "<<get<2>(t)<<", "<<get<3>(t)<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif

template<class T>
void self_max(T& x, T y) {
	x = max(x, y);
}

void solve() {
	int n;
	LL c;
	cin >> n >> c;
	vector<LL> a(n);
	vector<int> w(n);
	REP(i, n)
		cin >> a[i] >> w[i];
	debug(n, c, a, w);

	const int W = *max_element(w.begin(), w.end()) + 1;

	vector<LL> score(W);
	vector<pair<int, LL>> updates;
	LL best = 0;
	auto update = [&](int id, LL value) {
		debug(id, value);
		updates.emplace_back(id, value);
	};
	auto get_max = [&]() {
		return best;
	};
	auto get_value = [&](int id) {
		return score[id];
	};
	auto finish_turn = [&]() {
		for (auto [id, value] : updates) {
			score[id] = max(score[id], value);
			best = max(best, value);
		}
		updates.clear();
	};

	auto do_lr = [&](int l, int r) {
		FOR(i, l, r) {
			const int me = w[i];
			update(me, get_value(me) + a[i]);
			update(me, get_max() - c + a[i]);
		}
	};

	FOR(l, 0, n - 1) {
		int r = l + 1;
		while (r < n and a[r] == a[l])
			++r;
		--r;
		debug(l, r);
		//===============================================

		do_lr(l, r);

		//===============================================
		l = r;
		finish_turn();
	}

	cout << get_max() << '\n';
}

int main() {
	cin.tie(0)->sync_with_stdio(0);

	solve();
}