#include<bits/stdc++.h>

using namespace std;

#define setIO(s) freopen(s".in","r",stdin)

#define maxn 300000

#define inf 1000000

deque<int>p,q;

struct Node

{

    int x,y;

}nd[maxn];

bool cmp(Node a, Node b)

{

    return a.x < b.x;

}

int main()

{

    // setIO("input");

    int n,D,ans=inf;

    scanf("%d%d",&n,&D);

    for(int i=1;i<=n;++i)

    {

        scanf("%d%d",&nd[i].x,&nd[i].y);

    }

    sort(nd+1,nd+1+n,cmp);

    for(int i=1;i<=n;++i)

    {

        while(!p.empty()&&nd[i].y>=nd[p.back()].y) p.pop_back();

        while(!q.empty()&&nd[i].y<=nd[q.back()].y) q.pop_back();

        p.push_back(i), q.push_back(i);

        int pre=0;

        while(!p.empty()&&nd[p.front()].y-nd[i].y>=D) { pre=nd[p.front()].x;  p.pop_front(); }

        if(pre) ans=min(ans, nd[i].x - pre);

        pre=0;

        while(!q.empty()&&nd[i].y-nd[q.front()].y>=D) { pre=nd[q.front()].x;  q.pop_front(); }

        if(pre) ans=min(ans, nd[i].x - pre);

    }

    printf("%d\n",ans==inf?-1:ans);

    return 0;

}