#include <bits/stdc++.h>
using namespace std;
const int N = 202020;
inline char get(void) {
  static char buf[100000], *S = buf, *T = buf;
  if (S == T) {
    T = (S = buf) + fread(buf, 1, 100000, stdin);
    if (S == T) return EOF;
  }
  return *S++;
}
template <typename T>
inline void read(T &x) {
  static char c;
  x = 0;
  int sgn = 0;
  for (c = get(); c < '0' || c > '9'; c = get())
    if (c == '-') sgn = 1;
  for (; c >= '0' && c <= '9'; c = get()) x = x * 10 + c - '0';
  if (sgn) x = -x;
}
int n, m, ans;
int l[N], r[N];
vector<int> p[N];
int mx[N << 2], ad[N << 2];
inline void PushDown(int o) {
  if (ad[o]) {
    ad[o << 1] += ad[o];
    ad[o << 1 | 1] += ad[o];
    mx[o << 1] += ad[o];
    mx[o << 1 | 1] += ad[o];
    ad[o] = 0;
  }
}
inline void Add(int o, int l, int r, int L, int R, int x) {
  if (L > R) return;
  if (l >= L && r <= R) {
    ad[o] += x;
    mx[o] += x;
    return;
  }
  int mid = (l + r) >> 1;
  PushDown(o);
  if (L <= mid) Add(o << 1, l, mid, L, R, x);
  if (R > mid) Add(o << 1 | 1, mid + 1, r, L, R, x);
  mx[o] = max(mx[o << 1], mx[o << 1 | 1]);
}
inline int Query(int o, int l, int r, int L, int R) {
  if (L > R) return 0;
  if (l >= L && r <= R) return mx[o];
  int mid = (l + r) >> 1, res = 0;
  PushDown(o);
  if (L <= mid) res = max(res, Query(o << 1, l, mid, L, R));
  if (R > mid) res = max(res, Query(o << 1 | 1, mid + 1, r, L, R));
  return res;
}
inline void Build(int o, int l, int r) {
  if (l == r) return (void)(mx[o] = l - m + 1);
  int mid = (l + r) >> 1;
  Build(o << 1, l, mid);
  Build(o << 1 | 1, mid + 1, r);
  mx[o] = max(mx[o << 1], mx[o << 1 | 1]);
}
int main(void) {
  read(n);
  read(m);
  ++m;
  Build(1, 0, m);
  for (int i = 1; i <= n; i++) {
    read(l[i]);
    read(r[i]);
    p[l[i]].push_back(r[i]);
  }
  for (int i = 0; i <= m + 1; i++) {
    Add(1, 0, m, i, i, 1);
    if (p[i].size())
      for (int y : p[i]) Add(1, 0, m, i, y, 1);
    if (i && i <= m) ans = max(ans, Query(1, 0, m, i, m - 1) - i - 1);
    Add(1, 0, m, i, i, -1);
  }
  cout << ans << endl;
  return 0;
}
