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

#define ll long long
#define pb push_back
#define F first
#define S second
#define pii pair<int,int>
#define vi vector<int>
#define vpii vector<pii>

#define loop(i,n) sloop(0,i,n)
#define sloop(s, i, n) for(ll i=(s);i<(n);i++)
#define rloop(i,n) rsloop(0,i,n)
#define rsloop(s,i,n) for(ll i=(n);i-->(s);)

#define all(v) (v).begin(),(v).end()

#ifdef DEBUG
#define DBG cout << __LINE__ << endl;
#else 
#define DBG
#endif 

//int xses[8] = {-1,1,0,0,-1,1,1,-1};
//int yses[8] = {0,0,-1,1,-1,1,-1,1};

#define int ll

void solve()
{
	int n,c;
	cin >> n >> c;

	vpii v(n);
	loop(i,n)cin >> v[n-1-i].F >> v[n-1-i].S;

	vi dp(n);

	loop(i,n)dp[i]=v[i].F;

	//loop(i,n)cout << dp[i] << ' ';cout << endl;
	for(int i=0;i<n;i++)
	{
		for(int j=i-1;j>=0;j--)
		{
			dp[i] = max(dp[i],dp[j]+v[i].F-(v[i].S!=v[j].S?c:0));
		}
	}

	//loop(i,n)cout << dp[i] << ' ';cout << endl;
	cout << dp[n-1];



}

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

	int t=1;

	//cin >> t;

	while(t--)
		solve();

	return 0;
}