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#include <bits/stdc++.h>
using namespace std;

#define all(x) begin(x),end(x)
#define pb push_back
#define st first
#define nd second

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

const int INF = 2e9;
const ll LLINF = 2e18;

struct block
{
    ll a;
    int w;
};

void solve()
{
    int n,c;
    cin>>n>>c;
    vector<block> v(n);
    for(auto& b:v)
        cin>>b.a>>b.w;
    reverse(all(v));
    
    vector<ll> dp(n);
    unordered_map<int,ll> last_dp;
    vll use(n);
    for(auto b:v)
        last_dp[b.w] = 0;
    dp[0] = v[0].a;
    use[0] = v[0].a;
    last_dp[v[0].w] = dp[0];
    int i=1;
    while(i<n && v[i].a==v[i-1].a)
    {
        dp[i] = v[i].a;
        use[i] = v[i].a;
        last_dp[v[i].w] = max(last_dp[v[i].w], v[i].a);
        ++i;
    }


    while(i<n)
    {
        int j=i;
        while(j<n && v[j].a==v[i].a)
        {
            use[j] = max(dp[i-1]+v[j].a-c, last_dp[v[j].w]+v[j].a);
            dp[j] = max(dp[i-1], use[j]);
            ++j;
        }
        while(i<j)
        {
            last_dp[v[i].w] = max(last_dp[v[i].w], use[i]);
            dp[i] = max(dp[i], dp[i-1]);
            ++i;
        }
    }

    cout<<dp[n-1]<<"\n";
    /*for(auto x:use)
        cout<<x<<" ";
    cout<<"\n";
    for(auto x:dp)
        cout<<x<<" ";
    cout<<"\n";*/
}

int main()
{
    ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    int z=1;
    //cin>>z;
    while(z--)
        solve();
    return 0;
}