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#include <bits/stdc++.h>

#define ndl '\n'
#define ll long long
#define st first
#define nd second
#define debug(x) cout << #x << ": " << x << ndl
#define all(x) (x).begin(), (x).end()

using namespace std;



int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    int n, m; cin>>n>>m;
    vector<pair<ll, ll>> t(n);
    for(auto &[a, b]:t) cin>>a>>b;
    unordered_map<int, int> last_color;

    vector<ll> dp_lvl;
    vector<ll> dp(n);

    for(int i=0;i<n;i++) {
        if(i == 0 || t[i-1].first != t[i].first) {
            dp_lvl.push_back(0);
            if(i > 0) {
                dp_lvl.back() = max(dp_lvl.back(), dp_lvl[dp_lvl.size()-2]);
            }
        }

        dp[i] = max(dp[i], t[i].first);
        if(dp_lvl.size() > 1) {
            dp[i] = max(dp[i], dp_lvl[dp_lvl.size()-2] + t[i].first - m);
        }
        if(last_color.count(t[i].second) > 0) {
            if(t[last_color[t[i].second]].first != t[i].first) {
                dp[i] = max(dp[i], dp[last_color[t[i].second]] + t[i].first);
            } else {
                dp[i] = max(dp[i], dp[last_color[t[i].second]]);
            }
        }
        last_color[t[i].second] = i;
        dp_lvl.back() = max(dp_lvl.back(), dp[i]);
    }

    ll maxi = 0;
    for(auto x:dp) {
        maxi = max(maxi, x);
    }

    // for(auto x:dp) {
    //     cout<<x<<" ";
    // }

    // cout<<"\n";

    cout<<maxi<<'\n';
    return 0;

}