#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using uint = unsigned int;
#define rep(i,n) for(int i=0;i<int(n);i++)
#define rep1(i,n) for(int i=1;i<=int(n);i++)
#define per(i,n) for(int i=int(n)-1;i>=0;i--)
#define per1(i,n) for(int i=int(n);i>0;i--)
#define all(c) c.begin(),c.end()
#define si(x) int(x.size())
#define pb emplace_back
#define fs first
#define sc second
template<class T> using V = vector<T>;
template<class T> using VV = vector<vector<T>>;
template<class T,class U> void chmax(T& x, U y){if(x<y) x=y;}
template<class T,class U> void chmin(T& x, U y){if(y<x) x=y;}
template<class T> void mkuni(V<T>& v){sort(all(v));v.erase(unique(all(v)),v.end());}
template<class S,class T> ostream& operator<<(ostream& o,const pair<S,T> &p){
	return o<<"("<<p.fs<<","<<p.sc<<")";
}
template<class T> ostream& operator<<(ostream& o,const vector<T> &vc){
	o<<"{";
	for(const T& v:vc) o<<v<<",";
	o<<"}";
	return o;
}
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n-1); }

#ifdef LOCAL
#define show(x) cerr << "LINE" << __LINE__ << " : " << #x << " = " << (x) << endl
void dmpr(ostream& os){os<<endl;}
template<class T,class... Args>
void dmpr(ostream&os,const T&t,const Args&... args){
	os<<t<<" ~ ";
	dmpr(os,args...);
}
#define shows(...) cerr << "LINE" << __LINE__ << " : ";dmpr(cerr,##__VA_ARGS__)
#define dump(x) cerr << "LINE" << __LINE__ << " : " << #x << " = {";  \
	for(auto v: x) cerr << v << ","; cerr << "}" << endl;
#else
#define show(x) void(0)
#define dump(x) void(0)
#define shows(...) void(0)
#endif

template<class N>
struct segbeats{
	V<N> x;
	int s;

	segbeats(int n){
		s = 1;
		while(s<n) s *= 2;
		x.resize(s*2);
		for(int i=s-1;i>0;i--) upd(i);
	}
	template<class T>
	segbeats(const V<T>& a){
		int n = a.size();
		s = 1;
		while(s<n) s *= 2;
		x.resize(s*2);
		rep(i,n) x[s+i] = N(a[i]);
		for(int i=s-1;i>0;i--) upd(i);
	}

	template<class F,class... Args>
	void ch(int a,int b,F f,Args... args){
		ch_(a,b,0,s,1,f,args...);
	}

	template<class F,class G,class H>
	auto get(int a,int b,F f,G g,H h){
		return get_(a,b,0,s,1,f,g,h);
	}

	N getNode(int a,int b){
		return getNode_(a,b,0,s,1);
	}

	template<class F,class... Args>
	pair<int,N> findl(int a,int b,F f,Args&... args){
		return findl_(a,b,0,s,1,f,args...);
	}

	private:

	void push(int i){
		x[i].push(x[i*2],x[i*2+1]);
	}
	void upd(int i){
		x[i] = N::merge(x[i*2],x[i*2+1]);
	}

	template<class F,class... Args>
	void ch_(int a,int b,int l,int r,int i,F f,Args... args){
		if(b<=l || r<=a){
			return;
		}
		if(a<=l && r<=b && (x[i].*f)(args...)){    //f : put_tag, early_break
			return;
		}
		push(i);
		int m = (l+r)/2;
		ch_(a,b,l,m,i*2  ,f,args...);
		ch_(a,b,m,r,i*2+1,f,args...);
		upd(i);
	}
	template<class F,class G,class H>
	auto get_(int a,int b,int l,int r,int i,F f,G g,H h){
		if(b<=l || r<=a){
			return h;
		}
		if(a<=l && r<=b){
			return (x[i].*f)();
		}
		push(i);
		int m = (l+r)/2;
		return g(get_(a,b,l,m,i*2,f,g,h),get_(a,b,m,r,i*2+1,f,g,h));
	}
	N getNode_(int a,int b,int l,int r,int i){
		if(b<=l || r<=a){
			return N();
		}
		if(a<=l && r<=b){
			return x[i];
		}
		push(i);
		int m = (l+r)/2;
		return N::merge(getNode_(a,b,l,m,i*2),getNode_(a,b,m,r,i*2+1));
	}
	template<class F,class... Args>
	pair<int,N> findl_(int a,int b,int l,int r,int i,F f,Args&... args){
		if(b<=l || r<=a){
			return {b,N()};
		}
		if(a<=l && r<=b){
			if(!(x[i].*f)(args...)) return {b,N()};
			if(r-l == 1) return {l,x[i]};
		}
		push(i);
		int m = (l+r)/2;
		auto x = findl_(a,b,l,m,i*2,f,args...);
		if(x.fs < b) return x;
		return findl_(a,b,m,r,i*2+1,f,args...);
	}

	// template<class F,class... Args>
	// pair<int,N> findr_(int a,int b,int l,int r,int i,F f,Args&... args){
	// 	if(b<=l || r<=a){
	// 		return {a-1,N()};
	// 	}
	// 	if(a<=l && r<=b){
	// 		if(!(x[i].*f)(args...)) return {a-1,N()};
	// 		if(r-l == 1) return {l,x[i]};
	// 	}
	// 	push(i);
	// 	int m = (l+r)/2;
	// 	auto y = findr_(a,b,m,r,i*2+1,f,args...);
	// 	if(y.fs >= a) return y;
	// 	return findr_(a,b,l,m,i*2,f,args...);
	// }

};

struct D{
	int ad=0,mx=0;
	D(int v=0){mx=v;}
	static D merge(D l,D r){
		D z;
		z.mx = max(l.mx,r.mx);
		return z;
	}
	void push(D& x,D& y){
		x.ad += ad, x.mx += ad;
		y.ad += ad, y.mx += ad;
		ad = 0;
	}
	bool add(int x){
		ad += x, mx += x;
		return true;
	}
	int getmax(){
		return mx;
	}
};

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);		//DON'T USE scanf/printf/puts !!
	cout << fixed << setprecision(20);

	int N,M; cin >> N >> M;
	VV<int> l2rs(M+1);
	rep(i,N){
		int l,r; cin >> l >> r;
		r = M+1-r;
		l2rs[l].pb(r);
	}
	V<int> ini(M+1); rep(i,M+1) ini[i] = -i;
	segbeats<D> seg(ini);
	int ans = 0;
	rep(l,M+1){
		for(int r: l2rs[l]){
			seg.ch(r,M+1,&D::add,1);
		}
		chmax(ans,seg.get(0,M+1,&D::getmax,[&](int l,int r){return max(l,r);},0)-l);
	}
	cout << ans << endl;
}
