#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < int(n); i++)
#define rrep(i, n) for (int i = int(n) - 1; i >= 0; i--)
#define reps(i, n) for (int i = 1; i <= int(n); i++)
#define rreps(i, n) for (int i = int(n); i >= 1; i--)
#define repc(i, n) for (int i = 0; i <= int(n); i++)
#define rrepc(i, n) for (int i = int(n); i >= 0; i--)
#define repi(i, a, b) for (int i = int(a); i < int(b); i++)
#define repic(i, a, b) for (int i = int(a); i <= int(b); i++)
#define each(x, y) for (auto &x : y)
#define all(a) (a).begin(), (a).end()
#define bit32(x) (1 << (x))
#define bit64(x) (1ll << (x))

using namespace std;

using i32 = int;
using i64 = long long;
using f80 = long double;
using vi32 = vector<i32>;
using vi64 = vector<i64>;
using vf80 = vector<f80>;
using vstr = vector<string>;

inline void yes() { cout << "Yes" << '\n'; exit(0); }
inline void no() { cout << "No" << '\n'; exit(0); }
inline i64 gcd(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); if (a % b == 0) return b; return gcd(b, a % b); }
inline i64 lcm(i64 a, i64 b) { if (min(a, b) == 0) return max(a, b); return a / gcd(a, b) * b; }
template <typename T> class pqasc : public priority_queue<T, vector<T>, greater<T>> {};
template <typename T> class pqdesc : public priority_queue<T, vector<T>, less<T>> {};
template <typename T> inline void amax(T &x, T y) { if (x < y) x = y; }
template <typename T> inline void amin(T &x, T y) { if (x > y) x = y; }
template <typename T> inline T exp(T x, i64 n, T e = 1) { T r = e; while (n > 0) { if (n & 1) r *= x; x *= x; n >>= 1; } return r; }
template <typename T> istream& operator>>(istream &is, vector<T> &v) { each(x, v) is >> x; return is; }
template <typename T> ostream& operator<<(ostream &os, vector<T> &v) { rep(i, v.size()) { if (i) os << ' '; os << v[i]; } return os; }
void solve(); int main() { ios::sync_with_stdio(0); cin.tie(0); cout << fixed << setprecision(16); solve(); return 0; }

void solve() {
  int n;
  cin >> n;
  int rmin = 2e9, lmax = 0;
  vector<pair<int, int>> lr;
  rep(i, n) {
    int l, r;
    cin >> l >> r;
    r++;
    lr.emplace_back(l, r);
    amin(rmin, r);
    amax(lmax, l);
  }
  int ans = 0;
  {
    int sum = 0;
    sum += max(rmin - lmax, 0);
    int ma = 0;
    rep(i, n) {
      int l, r;
      tie(l, r) = lr[i];
      amax(ma, r - l);
    }
    sum += ma;
    ans = sum;
  }
  {
    sort(all(lr));
    reverse(all(lr));
    int rr = lr[0].second;
    reps(i, n - 1) {
      int l, r;
      tie(l, r) = lr[i];
      amax(ans, max(rmin - l, 0) + max(rr - lmax, 0));
      amin(rr, r);
    }
  }
  cout << ans << endl;
}

#include<iostream>
#include<iomanip>
#include<cstdio>
#include<algorithm>
#include<cassert>
#include<cmath>
#include<vector>
#include<map>
#include<set>
#include<string>
#include<queue>
#include<stack>
#include<list>
#include <cstring>
#include <functional>
#include<unordered_map>
#include<unordered_set>
#include<bitset>
using namespace std;
#define MOD 1000000007
#define MOD2 998244353
#define INF ((1<<30)-1)
#define LINF ((Int)1<<60)
#define EPS (1e-10)
#define REP(i,n) for(int i=0; i<(int)(n); ++i)
#define RREP(i,n) for(int i=1; i<=(int)(n); ++i)
#define FOR(i,k,n) for(int i=(k);i<(int)(n);++i)
typedef long long Int;
typedef pair<Int, Int> PI;
typedef pair<int, int> P;
typedef vector<double> vec;
typedef vector<vec> mat;
const int N = 100005;
//////////////////////////////

int n, T;
P a[3300];
int dp[3300][3300];

void solve()
{
	cin >> n >> T;
	REP(i, n) {
		cin >> a[i].first >> a[i].second;
	}
	sort(a, a + n);

	for (int i = 0; i < n; i++) {
		for (int t = 0; t < T; t++) {
			dp[i + 1][t] = max(dp[i + 1][t], dp[i][t]);
			if (t - a[i].first >= 0) dp[i + 1][t] = max(dp[i + 1][t], dp[i][t - a[i].first] + a[i].second);
		}
	}

	int ans = 0;
	for (int i = 0; i < n; i++) {
		ans = max(ans, dp[i][T - 1] + a[i].second);
	}

	cout << ans << endl;
}

int main() {
	ios_base::sync_with_stdio(0); cin.tie(0); cout << fixed << setprecision(13);
	solve();
	return 0;
}
