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


using namespace std;

int main()
{
    int n, c;
    cin>>n>>c;
    vector<int> A(n+1), W(n+1);
    A[0]=0; W[0]=-1;
    for (int i=1; i<=n; i++){
        cin>>A[i]>>W[i];
    }
    unordered_map<int, int> last_seen;
    last_seen.reserve(W.size()+10);
    for (int i=1; i<last_seen.size();i++){
        last_seen[W[i]] = 0;
    }

    vector <int64_t> bests(n+1); //best score if the tower ends at i-th brick;

    bests[0] = 0;
    int64_t best=0;
    int i=0;

    while ( i< n ){
        int j=i+1;
        while( j<n && A[j]==A[j+1])
            j++;
        for (int k=i+1; k<=j; k++){
            int64_t ugly = A[k] + best -c;
            int64_t pretty = A[k] + bests[last_seen[W[k]]];
            bests[k]=max(ugly, pretty);
        }
        for (int k=i+1; k<=j; k++){
            if (bests[k]>best)
                best = bests[k];
            last_seen[W[k]]=k;
        }
        i=j;
    }
    cout<<best<<endl;

    return 0;
}