记录：https://www.luogu.com.cn/record/172207650

#include<iostream>
#include<algorithm>
#include<cmath>
#define rep(i,l,r) for(int i=l;i<=r;++i)
#define Rep(i,l,r) for(int i=l;i>=r;--i)
using std::cin;
using std::cout;
using std::min;
using std::max;
using std::sort;

int n,d,mxn=0;
const int N=1e6+1;
struct node{
	int x,y;
}t[N];
int st[N][21][2];
bool operator<(const node&a,const node&b){
	return a.y<b.y;
}
inline int query(int l,int r,bool lim){
	int k=log2(r-l+1);
	if(lim){
		return max(st[l][k][1],st[r-(1<<k)+1][k][1]);
	}else{
		return min(st[l][k][0],st[r-(1<<k)+1][k][0]);
	}
}
bool check(int mid){
	rep(i,0,mxn-mid+1){
		int c=query(i,i+mid-1,1)-query(i,i+mid-1,0);
		if(c>=d) return true;
	}
	return false;
}
int main(){
//	freopen("P2698_2.in","r",stdin);
	std::ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	cin>>n>>d;
	rep(i,1,n){
		cin>>t[i].x>>t[i].y;
		mxn=max(mxn,t[i].x);
	}
	sort(t+1,t+n+1);
	rep(i,1,n){
		st[t[i].x][0][0]=t[i].y;
		st[t[i].x][0][1]=t[i].y;
	}
	rep(j,1,20){
		for(int i=0;i+(1<<j)-1<=mxn;++i){
			st[i][j][0]=min(st[i][j-1][0],st[i+(1<<(j-1))][j-1][0]);
			st[i][j][1]=max(st[i][j-1][1],st[i+(1<<(j-1))][j-1][1]);
		}
	}
	int l=1,r=mxn,ans=0;
	while(l<=r){
		int mid=(l+r)>>1;
		if(check(mid)){
			r=mid-1;ans=mid;
		}else{
			l=mid+1;
		}
	}
	if(ans) cout<<ans<<'\n';
	else cout<<"-1\n";
	return 0;
}
//tomxi