//~~~~~~~~~~~~~MJ®™~~~~~~~~~~~~~
#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#define rep1(n) for(ll i=0; i<(ll)(n); ++i)
#define rep2(i,n) for(ll i=0; i<(ll)(n); ++i)
#define rep3(i,a,b) for(ll i=(ll)(a); i<(ll)(b); ++i)
#define rep4(i,a,b,c) for(ll i=(ll)(a); i<(ll)(b); i+=(c))
#define cut4(a,b,c,d,e,...) e
#define rep(...) cut4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define per1(n) for(ll i=((ll)n)-1; i>=0; --i)
#define per2(i,n) for(ll i=((ll)n)-1; i>=0; --i)
#define per3(i,a,b) for(ll i=((ll)a)-1; i>=(ll)(b); --i)
#define per4(i,a,b,c) for(ll i=((ll)a)-1; i>=(ll)(b); i-=(c))
#define per(...) cut4(__VA_ARGS__,per4,per3,per2,per1)(__VA_ARGS__)
#define ll long long
#define ln cout<<endl
#define int long long
#define Code ios_base::sync_with_stdio(0);
#define by cin.tie(NULL);
#define Hayan cout.tie(NULL);
#define append push_back
#define all(x) (x).begin(),(x).end()
#define allr(x) (x).rbegin(),(x).rend()
#define vi vector<int>
#define ret(x) {cout<<x;return;}
#define ui map<int,int>
#define pi pair<int,int>
#define ff first
#define ss second
using namespace std;
template <typename T> using v = vector<T>;
const int INF = 1e18, MOD = 1e9+7, N = 2e5+7;
const int lg= 20;
ll sp[N][lg];
ll mxt[N][lg];
int m;
ll get(int l, int r)
{
ll ch = 31 - __builtin_clz(r-l+1);
return max(mxt[l][ch], mxt[r-(1ll<<ch)+1][ch]);
}
// Function to initialize the Sparse Table
int tilmx[N];
vector<pi> a;
bool app(int k, int binary)
{
int l=k;
for (int i = 0; i < lg; i++)
{
int mask = 1LL << i;
if ((binary & mask) != 0)
{
k = sp[k][i];
}
}
// cout <<k<<" "<<l<<endl;
// cout << tilmx[k] << " " <<a[l].ff<< endl;
return (get(l,k)-a[l].ff)>=m;
}
void preprocess(int n)
{
for (int p = 1; p < lg; p++)
{
for (int i = 0; i < n; i++)
{
sp[i][p] = sp[sp[i][p - 1]][p - 1];
}
}
}
// Function to initialize the Sparse Table
void init(vector<pi>& ls)
{
ll n = ls.size();
for (int i=0; i<n; i++)
{
mxt[i][0] = ls[i].ss;
}
for (int i=1; i<lg; i++)
{
for (int j=0; j+(1ll<<i)<=n; j++)
{
mxt[j][i] = max(mxt[j][i-1], mxt[j+(1ll<<(i-1))][i-1]);
}
}
}
// Function to get the minimum value in the range [l, r]
void solve()
{
int n, k, e, ans = INF;
cin >> n >> m;
a.assign(n,{});
rep(n)
{
cin >> a[i].ff >> a[i].ss;
if (a[i].ff>a[i].ss)a[i].ss+=m;
a[i].ff+=m;
a[i].ss+=m;
}
// cout <<a[0].ff<<endl;
vi dp(n);
sort(all(a));
int mn,mx;
// n*=2;
rep(n)
{
tilmx[i]=a[i].ss;
if (i>0)
tilmx[i]=max(tilmx[i-1],tilmx[i]);
int op =1;
mn=a[i].ff;
mx=a[i].ss;
int j=i+1;
int k=0;
set<int> ax;
ax.insert(mx);
int maxj = (--upper_bound(all(a),(pi){mx,INF}) - a.begin());
if (maxj==-1) maxj=i;
sp[i][0]=maxj;
}
preprocess(n);
init(a);
rep(n)
{
int l=0,r=n+1;
while (r-l>1)
{
int mid=(r+l)/2;
if (app(i,mid))
{
r=mid;
}
else l=mid;
}
if(app(i,r))
{
// cout <<i<< " "<<r<<endl;
ans=min(ans,r);
}
}
// cout <<app(0,3)<<endl;
// rep(4)
// {
// rep(j,0,4)
// {
// if (j>=i)
// cout <<get(i,j)<<" ";
// // else cout <<"000"<<" ";
// }ln;
// }
cout << (ans==INF ? -1: ans+1);ln;
// cout << a.size();
// k=0;
// for (auto i: a){cout << i.ff << " " <<i.ss<<" "<<sp[k][0]<<" "<<tilmx[k++];ln;}
}
signed main(){
Code by Hayan
int ans=1;
//cout<<setprecision(1000);
// cin>>ans;
rep(ans){
// cout << "Case #" << i+1 << ": ";
solve();ln;}}
