#include<bits/stdc++.h>
using namespace std;
struct node{
	int x,y;
}a[100001];
int n,d,ans=0x7f7f;
priority_queue<int> que1;
priority_queue<int,vector<int>,greater<int> >que2;
bool cmp(node g1,node g2){
	return g1.y<g2.y;
}
int main(){
	freopen("double_muscle.in","r",stdin);
	freopen("double_muscle.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>d;
	for(int i=1;i<=n;++i){
		cin>>a[i].x>>a[i].y;
	}
	sort(a+1,a+1+n,cmp);
	int j=1;
	for(int i=2;i<=n;++i){
		int down=a[i].y-d; 
		while(a[j].y<=down){
			que1.push(a[j].x);
			++j;
		}
		if(!que1.empty()){
		    while(que1.top()>a[i].x){
			    que2.push(que1.top());
			    que1.pop();
			    if(que1.empty()){
			    	break;
			    }
		    }
		}
		if(!que2.empty()){
			while(que2.top()<a[i].x){
				que1.push(que2.top());
				que2.pop();
				if(que2.empty()){
					break;
				}
			}
		}
		if(!que1.empty()){
			ans=min(ans,a[i].x-que1.top());
		}
		if(!que2.empty()){
			ans=min(ans,que2.top()-a[i].x);
		}
    }
    if(ans<0x7f7f){
    	cout<<ans<<endl;
    }
    else{
    	cout<<"-1"<<endl;
    }
    return 0;
}