#include <bits/stdc++.h>
using namespace std;
const int N=100000+5;
const int inf=0x7fffffff;
int n,m;
struct xcv{
    int x,y;
}p[N];
struct sdf{
    int l,r,mn,mx;
}tr[4*N];
bool cmp(xcv a,xcv b){
    return a.x<b.x;
}
void update(int pt){
    tr[pt].mn=min(tr[pt*2].mn,tr[pt*2+1].mn);
    tr[pt].mx=max(tr[pt*2].mx,tr[pt*2+1].mx);
    return ;
}
void build(int pt,int l,int r){
    tr[pt]={l,r,inf,0};
    if (l==r){
        tr[pt].mn=tr[pt].mx=p[l].y;return ;
    }
    int mid=(l+r)/2;
    build(pt*2,l,mid);build(pt*2+1,mid+1,r);
    update(pt);
    return ;
}
struct wer{
    int mn,mx;
};
wer ask(int pt,int l,int r){
    if (l>r)return {0,0};
    if (l<=tr[pt].l&&tr[pt].r<=r)return {tr[pt].mn,tr[pt].mx};
    int mid=(tr[pt].l+tr[pt].r)/2;
    wer now={inf,0},tmp;
    if (l<=mid){
        tmp=ask(pt*2,l,r);
        now.mn=min(now.mn,tmp.mn);now.mx=max(now.mx,tmp.mx);
    }
    if (mid+1<=r){
        tmp=ask(pt*2+1,l,r);
        now.mn=min(now.mn,tmp.mn);now.mx=max(now.mx,tmp.mx);
    }
    return now;
}
int main(){
    freopen ("double_muscle.in","r",stdin);
    freopen ("double_muscle.out","w",stdout);
    scanf("%d%d",&n,&m);
    for (int i=1;i<=n;i++){
        scanf("%d%d",&p[i].x,&p[i].y);
    }
    sort(p+1,p+n+1,cmp);
    build(1,1,n);
    int l=1,r=0,ans=inf;wer now;
    while(l<=n){
        now=ask(1,l,r);
        if (now.mx-now.mn<m&&r!=n){
            r++;
        }
        else{
            if (now.mx-now.mn>=m)ans=min(ans,p[r].x-p[l].x);
            else if (r==n)break;
            l++;
        }
    }
    if (ans==inf)printf("-1\n");
    else printf("%d\n",ans);
    return 0;
}