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#include <bits/stdc++.h>


using namespace std;
#define ll long long
#define ld long double
#define all(a) (a).begin(), (a).end()
#define allr(a) (a).rbegin(), (a).rend()
#define F first
#define S second
#define pb push_back
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

/*
#ifndef ONLINE_JUDGE
#include <cpp-dump.hpp>
#endif
*/

constexpr ll mod = 1e9+7;

ll power(ll a, ll b){
    ll res = 1;
    while(b){
        if(b&1) res = res * a % mod;
        a = a * a % mod;
        b >>= 1;
    }
    return res;
}

/*
ll fact[300001];
ll C(ll n, ll k){
    if(k < 0 || k > n) return 0;
    return fact[n] * power(fact[k], mod-2) % mod * power(fact[n-k], mod-2) % mod;
}
*/

struct Max {
    ll operator()(ll a, ll b) const {
        return max(a, b);
    }
};


template<typename T = int, typename Op = std::plus<T>>
struct TreePS
{
    TreePS(const std::vector<T> &data, T identity) : identity_(identity){
        this->size = 1;
        while(this->size < data.size())
            this->size<<=1;
        this->data.resize(this->size * 2, identity_);
        for (size_t i = 0; i < data.size(); i++)
            this->data[this->size + i] = data[i];
        for(size_t i = size-1; i > 0; i--)
            this->data[i] = Op()(this->data[2*i], this->data[2*i+1]);
    }
    TreePS(size_t size, T value, T identity) : identity_(identity){
        this->size = 1;
        while(this->size < size)
            this->size<<=1;
        this->data.resize(this->size * 2, identity_);
        for(size_t i = size; i < 2*size; i++)
            this->data[i] = value;
        for(size_t i = size-1; i > 0; i--)
            this->data[i] = Op()(this->data[2*i], this->data[2*i+1]);
    }
    T query(size_t l, size_t r) const
    {
        size_t lpos = l + this->size, rpos = r + 1 + this->size;
        T res = identity_;
        while(lpos < rpos){
            if(lpos&1){
                res = Op()(res, this->data[lpos]);
                lpos++;
            }
            if(rpos&1){
                rpos--;
                res = Op()(res, this->data[rpos]);
            }
            lpos>>=1;
            rpos>>=1;
        }
        return res;
    }
    void update(size_t i, T value){
        size_t pos = i + this->size;
        this->data[pos] = Op()(this->data[pos],value);
        pos >>= 1;
        while(pos > 0){
            this->data[pos] = Op()(this->data[2*pos], this->data[2*pos+1]);
            pos>>=1;
        }
    }
    size_t size;
    T identity_;
    std::vector<T> data;
};

void dzik77() {

    ll n, c; cin >> n >> c;
	vector<pll> dp(500'001,{0,-1});
    TreePS<ll, Max> tree(500'001, 0, 0);
    ll ans = 0;
	for (int i = 0; i < n; i++){
		ll a, w; cin >> a >> w;
		if (dp[w].second < a) {
            dp[w] = {dp[w].first + a, a};
        }
        ll res = tree.query(0, a-1);
        if(dp[w].first < res + a - c){
            dp[w].first = res + a - c;
            dp[w].second = a;
        }
        tree.update(a, dp[w].first);
        ans = max(ans, dp[w].first);
	}
	cout << ans << '\n';
    
}

int32_t main()
{

    ios::sync_with_stdio(0);
    cin.tie(0);

    /*
    fact[0] = 1;
    for (int i = 1; i < 300001; i++){
        fact[i] = fact[i-1] * i % mod;
    }
    */

    int t = 1;
    //cin >> t;
    while(t--)
		dzik77();

    return 0;
}