#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

const int N = 5e5 + 5;

pair<int, int> Blocks[N];

ll Best[N];
ll TempBest[N];

ll Solve(int n, int c)
{
    ll sol = 0, temp = 0;
    int last = 1;

    for(int i = 1; i <= n; i++) {
        auto [a, w] = Blocks[i];

        if(a != Blocks[i-1].first) {
            for(int j = last; j < i; j++)
                Best[Blocks[j].second] = TempBest[Blocks[j].second];
            
            last = i;
            sol = max(sol, temp);
            temp = 0;
        }

        ll x = Best[w] + a;
        ll y = sol + a - c;

        TempBest[w] = max(x, y);
        temp = max({temp, x, y});
    }
    return max(sol, temp);
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int n, c, a, w;
    cin >> n >> c;

    for(int i = 1; i <= n; i++)
        cin >> Blocks[i].first >> Blocks[i].second;
    cout << Solve(n, c) << "\n";

    return 0;
}