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#include <bits/stdc++.h>
using namespace std;
#define rep(a, b) for (int a = 0; a < (b); a++)
#define rep1(a, b) for (int a = 1; a <= (b); a++)
#define all(x) (x).begin(), (x).end()
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int MOD = 1e9 + 7;

#define LOCAL false

const int LIM = 5e5 + 7;
int n, c;

pair<int, int> vals[LIM];
ll best1=0;
ll best2=0;
ll curh=0;
ll best1c[LIM];
ll best2c[LIM];
ll curhc[LIM];

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    if (LOCAL) {
        ignore=freopen("io/in", "r", stdin);
        ignore=freopen("io/out", "w", stdout);
    }

    cin >> n >> c;
    rep1(i, n) cin >> vals[i].first >> vals[i].second;
    reverse(vals+1, vals+1+n);
    
    ll out = 0;
    rep1(i, n) {
        auto [h, col] = vals[i];
        ll ans = -1;
        if (h != curh) ans = max(ans, h+best1-c);
        else ans = max(ans, h+best2-c);
        if (h != curhc[col]) ans = max(ans, h+best1c[col]);
        else ans = max(ans, h+best2c[col]);
        
        if (ans > best1) {
            if (h != curh) {
                best2 = best1;
                best1 = ans;
                curh = h;
            } else best1 = ans;
        }
        if (ans > best1c[col]) {
            if (h != curhc[col]) {
                best2c[col] = best1c[col];
                best1c[col] = ans;
                curhc[col] = h;
            } else best1c[col] = ans;
        }
        out = max(out, ans);
    }
    cout << out << "\n";

    return 0;
}