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#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

#define int long long

const int maxx = 5e5+7;
const int base = 1 << 19;

vector<pair<int,int>>last[maxx];
pair<int,int>tre[base << 1];

void add(int v, int hight, int color){
    v+=base;
    tre[v] = {hight,color};
    while(v){
        v/=2;
        //tre[v] = tre[2*v] ^ tre[2*v+1];
        if(tre[2*v].first > tre[2*v+1].first){
            tre[v] = tre[2*v];
        }else{
            tre[v] = tre[2*v+1];
        }
    }
}
pair<int,int> que(int a, int b){
    pair<int,int>res = {0,0};
    a +=base -1;
    b +=base +1;
    while(b>a+1){
        if(!(a&1)){
            //wyni ^= tre[a + 1];
            if(res.first < tre[a+1].first){
                res = tre[a+1];
            }
        }
        if(b&1){
            //wyni ^= tre[b - 1];
            if(res.first < tre[b-1].first){
                res = tre[b-1];
            }
        }
    a/=2;
    b/=2;
    }
    return res;
}

signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n; cin>>n;
    int c; cin>>c;
    vector<pair<int,int>>in(n+1,{0,0});
    for(int i=1; n>=i; i++){
        pair<int,int>tmp;
        cin>>tmp.first>>tmp.second;
        in[i] = tmp;
    }
    reverse(in.begin()+1,in.end());

    // cout<<endl;for(auto x : in){
    //     cout<<x.first<<" "<<x.second<<endl;
    // }cout<<endl;

    pair<int,int>wsk = {in[1].first,0};
    for(int i=1; n>=i; i++){
        if(in[i].first < wsk.first){
            wsk = {in[i].first,i-1};
        }
        pair<int,int>tmp = que(0,wsk.second);

        // sprawdzam dwa poprzednie klocki o tym samym kolorze
        if(last[in[i].second].size() == 0){
            last[in[i].second].push_back({in[i].first,i});
            int maxi = max(in[i].first, tmp.first + in[i].first - c);
            add(i,maxi,in[i].second);
            //last[in[i].second].push_back({maxi,i});
        }else if(last[in[i].second].size() == 1){
            int maxi = in[i].first;
            if(last[in[i].second][0].first > in[i].first){
                pair<int,int>tmp2 = que(last[in[i].second][0].second,last[in[i].second][0].second);
                maxi = max(tmp2.first + in[i].first, tmp.first + in[i].first - c);
                add(i,maxi,in[i].second);
                last[in[i].second].push_back({in[i].first,i});
            }else{
                maxi = max(in[i].first, tmp.first + in[i].first - c);
                add(i,maxi,in[i].second);
            }
        }else{
            int maxi = in[i].first;
            if(last[in[i].second][1].first > in[i].first){
                pair<int,int>tmp2 = que(last[in[i].second][1].second,last[in[i].second][1].second);
                maxi = max(tmp2.first + in[i].first, tmp.first + in[i].first - c);
                add(i,maxi,in[i].second);
                swap(last[in[i].second][1],last[in[i].second][0]);
                last[in[i].second][1] = {in[i].first, i};
            }else{
                pair<int,int>tmp2 = que(last[in[i].second][0].second,last[in[i].second][0].second);
                maxi = max(tmp2.first + in[i].first, tmp.first + in[i].first - c);
                add(i,maxi,in[i].second);
            }
        }
        //wypisywanie maksymalnej wartosci na ten moment
        // cout<<"rozwzany klocek: "<<in[i].first<<" "<<in[i].second<<endl;
        // cout<<"maksymalny wstecz: "<<tmp.first<<" "<<tmp.second<<endl;
        // tmp = que(i,i);
        // cout<<"wynik na ten moment: "<<tmp.first<<" "<<tmp.second<<endl<<endl;
    }
    int maxi = -1;
    for(int i=1; n>=i; i++){
        maxi = max(maxi, que(i,i).first);
    }
    cout<<maxi;
}

/*

4 1
1 1
3 2
4 3
4 1

4 5
1 1
3 2
4 4
4 4


4 5
1 1
3 2
4 3
4 1

*/