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#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for (int i = (a); i <= (b); ++i)
#define REPD(i,a,b) for (int i = (a); i >= (b); --i)
#define FORI(i,n) REP(i,1,n)
#define FOR(i,n) REP(i,0,int(n)-1)
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define SZ(x) int((x).size())
#define DBG(v) cerr << #v << " = " << (v) << endl;
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define fi first
#define se second

const int N = 500500;

int n,c;
int a[N], w[N];
ll best[N];
int last_a[N];

int main() {
	scanf("%d%d", &n, &c);
	FORI(i,n) scanf("%d%d", &a[i], &w[i]);
	ll global_score = 0, local_score = 0;
	FORI(i,n) {
		ll cur_score = max(0LL, global_score - c);
		if (last_a[w[i]] != a[i]) cur_score = max(cur_score, best[w[i]]);
		cur_score += a[i];
		best[w[i]] = max(best[w[i]], cur_score);
		last_a[w[i]] = a[i];
		local_score = max(local_score, cur_score);
		//printf("%d : %lld %lld %lld\n", i, cur_score, local_score, global_score);
		if (i == n || a[i] != a[i+1]) {
			global_score = max(global_score, local_score);
		}
	}
	printf("%lld\n", global_score);
	return 0;
}