def main(): import sys input = sys.stdin.readline d, q = map(int, input().split()) rs = RangeSet() ans = 0 for _ in range(q): a, b = map(int, input().split()) rs.add(a, b + 1) l, r = rs.covered_by(a, a + 1) ans = max(ans, r - l) print(ans) # https://github.com/tatyam-prime/SortedSet/blob/main/SortedSet.py import math from bisect import bisect_left, bisect_right from typing import Generic, Iterable, Iterator, List, Tuple, TypeVar, Optional T = TypeVar("T") class SortedSet(Generic[T]): BUCKET_RATIO = 50 REBUILD_RATIO = 170 def _build(self, a: Optional[List[T]] = None) -> None: "Evenly divide `a` into buckets." if a is None: a = list(self) size = len(a) bucket_size = int(math.ceil(math.sqrt(size / self.BUCKET_RATIO))) self.a = [ a[size * i // bucket_size : size * (i + 1) // bucket_size] for i in range(bucket_size) ] def __init__(self, a: Iterable[T] = []) -> None: "Make a new SortedSet from iterable. / O(N) if sorted and unique / O(N log N)" a = list(a) self.size = len(a) if not all(a[i] < a[i + 1] for i in range(len(a) - 1)): a = sorted(set(a)) self._build(a) def __iter__(self) -> Iterator[T]: for i in self.a: for j in i: yield j def __reversed__(self) -> Iterator[T]: for i in reversed(self.a): for j in reversed(i): yield j def __eq__(self, other) -> bool: return list(self) == list(other) def __len__(self) -> int: return self.size def __repr__(self) -> str: return "SortedSet" + str(self.a) def __str__(self) -> str: s = str(list(self)) return "{" + s[1 : len(s) - 1] + "}" def _position(self, x: T) -> Tuple[List[T], int]: "Find the bucket and position which x should be inserted. self must not be empty." for a in self.a: if x <= a[-1]: break return (a, bisect_left(a, x)) def __contains__(self, x: T) -> bool: if self.size == 0: return False a, i = self._position(x) return i != len(a) and a[i] == x def add(self, x: T) -> bool: "Add an element and return True if added. / O(√N)" if self.size == 0: self.a = [[x]] self.size = 1 return True a, i = self._position(x) if i != len(a) and a[i] == x: return False a.insert(i, x) self.size += 1 if len(a) > len(self.a) * self.REBUILD_RATIO: self._build() return True def _pop(self, a: List[T], i: int) -> T: ans = a.pop(i) self.size -= 1 if not a: self._build() return ans def discard(self, x: T) -> bool: "Remove an element and return True if removed. / O(√N)" if self.size == 0: return False a, i = self._position(x) if i == len(a) or a[i] != x: return False self._pop(a, i) return True def lt(self, x: T) -> Optional[T]: "Find the largest element < x, or None if it doesn't exist." for a in reversed(self.a): if a[0] < x: return a[bisect_left(a, x) - 1] def le(self, x: T) -> Optional[T]: "Find the largest element <= x, or None if it doesn't exist." for a in reversed(self.a): if a[0] <= x: return a[bisect_right(a, x) - 1] def gt(self, x: T) -> Optional[T]: "Find the smallest element > x, or None if it doesn't exist." for a in self.a: if a[-1] > x: return a[bisect_right(a, x)] def ge(self, x: T) -> Optional[T]: "Find the smallest element >= x, or None if it doesn't exist." for a in self.a: if a[-1] >= x: return a[bisect_left(a, x)] def __getitem__(self, i: int) -> T: "Return the i-th element." if i < 0: for a in reversed(self.a): i += len(a) if i >= 0: return a[i] else: for a in self.a: if i < len(a): return a[i] i -= len(a) raise IndexError def pop(self, i: int = -1) -> T: "Pop and return the i-th element." if i < 0: for a in reversed(self.a): i += len(a) if i >= 0: return self._pop(a, i) else: for a in self.a: if i < len(a): return self._pop(a, i) i -= len(a) raise IndexError def index(self, x: T) -> int: "Count the number of elements < x." ans = 0 for a in self.a: if a[-1] >= x: return ans + bisect_left(a, x) ans += len(a) return ans def index_right(self, x: T) -> int: "Count the number of elements <= x." ans = 0 for a in self.a: if a[-1] > x: return ans + bisect_right(a, x) ans += len(a) return ans class RangeSet: def __init__(self, inf=float("inf")) -> None: self.inf = inf self.st = SortedSet([(-inf, -inf), (inf, inf)]) self.sum = 0 def getindex(self, i) -> int: return self.st.index((i, self.inf)) - 1 def getitem(self, i) -> int: return self.st.le((i, self.inf)) def add(self, l: int, r: int) -> int: # 半開区間[l, r)を追加する # 追加した区間数を返す assert l <= r i, j = self.getitem(l) if i <= l and r <= j: return 0 res = 0 idx = self.getindex(l) if i <= l and l <= j: res -= j - i l = i self.st.pop(idx) else: idx += 1 while r > self.st[idx][1]: i, j = self.st[idx] res -= j - i self.st.pop(idx) if self.st[idx][0] <= r: i, j = self.st[idx] res -= j - i self.st.pop(idx) r = j self.st.add((l, r)) res += r - l self.sum += res return res def remove(self, l: int, r: int) -> int: # 半開区間[l, r)を削除する # 削除した区間数を返す assert l <= r i, j = self.getitem(l) idx = self.getindex(l) if i <= l and r <= j: self.st.pop(idx) if i < l: self.st.add((i, l)) if r < j: self.st.add((r, j)) res = r - l self.sum -= res return res res = 0 if i <= l and l < j: res += j - l self.st.pop(idx) if i < l: self.st.add((i, l)) idx += 1 else: idx += 1 while self.st[idx][1] <= r: i, j = self.st[idx] res += j - i self.st.pop(idx) if self.st[idx][0] < r: i, j = self.st[idx] res += r - i self.st.pop(idx) self.st.add((r, j)) self.sum -= res return res def covered(self, l: int, r: int) -> bool: assert l <= r i, j = self.getitem(l) return i <= l and r < j def covered_by(self, l: int, r: int) -> bool: assert l <= r i, j = self.getitem(l) if i <= l and r <= j: return i, j return None, None def size(self) -> int: return self.sum def mex(self, m: int = 0) -> int: # m以上で範囲外の最小の整数を返す i, j = self.getitem(m) if i <= m and m < j: return j return m def get_all(self): return tuple(self.st)[1:-1] def __repr__(self) -> str: s = str(self.get_all()) return "RangeSet{" + s[1:-1] + "}" def __str__(self) -> str: s = str(self.get_all()) return "{" + s[1:-1] + "}" if __name__ == "__main__": main()