/****ThanhCodeDao*****/
/*******Azazel*******/
#include<bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define pb push_back
#define checkbit(mask,i) ((mask>>i)&1)
#define bit(i) (1<<i)
#define MLog 18
#define all(v) v.begin(), v.end()
#define uni(v) v.erase(unique(all(v)), v.end())
typedef long long ll;
const ll maxN = 5e5+36, modd = 1e9+7;
struct Point {
ll x,y;
};
ll cross(Point p,Point q,Point r) { // vi tri r voi duong pq >0 la ben trai, =0 la thang hang
ll val = (q.x-p.x)*(r.y-q.y) - (q.y-p.y)*(r.x-q.x);
if(val < 0) return -1;
if(val > 0) return 1;
return 0;
}
ll dot(Point vecA,Point vecB) { // tra ve >0 la nhon, <0 la tu, =0 la vuong, 2 vecto phai chung goc
ll val = vecA.x*vecB.x + vecA.y*vecB.y;
if(val < 0) return -1;
if(val > 0) return 1;
return 0;
}
double triarea(Point p,Point q,Point r) { // cross(pq * pr) / 2
double cross = (q.x-p.x)*(r.y-q.y) - (q.y-p.y)*(r.x-q.x);
return fabs(cross)/2.0;
}
/* de cho
*/
/* nhan xet nho
*/
/* nhan xet tu thuat trau
*/
int n,m;
pair<int,int> p[maxN];
bool cmp(pair<int,int> p1, pair<int,int> p2) {
if(p1.F == p2.F) {
return p1.S > p2.S;
}
return p1.F < p2.F;
}
int ans = 1e9;
void dfs(int i,int finish,int &cnt,bool &isfinish) {
int j = i;
int mxr = 0, curchose = 0;
while(j+1<=n and p[i].F <= p[j+1].F and p[j+1].F <= p[i].S) {
if(p[j+1].S > mxr) {
mxr = p[j+1].S;
curchose = j+1;
}
++j;
}
++cnt;
if(cnt >= ans) return ;
if(i>n) return;
if(mxr >= finish) {
isfinish = true;
return;
} else {
if(curchose == 0) {
isfinish = false;
return;
}
dfs(curchose,finish,cnt,isfinish);
}
}
void sub3() {
for(int i = 1; i<=n; i++) {
bool isend = false;
int cnt = 1;
dfs(i,p[i].F + m,cnt,isend);
if(isend) {
ans = min(ans,cnt);
}
}
if(ans == 1e9) ans = -1;
cout << ans;
}
vector<int> compress;
struct node{
int r,id;
node operator + (const node & other){
node res;
res.r =max(r, other.r);
if(r > other.r) {
res.id = id;
}else{
res.id = other.id;
}
return res;
}
} tree[maxN*4];
void up(int id,int l,int r,int idx,pair<int,int> val){
if(idx < l || r < idx || l > r) return;
if(l==r){
tree[id].r = val.F;
tree[id].id = val.S;
return;
}
int mid = (l+r)/2;
up(2*id,l,mid,idx,val);
up(2*id+1,mid+1,r,idx,val);
tree[id] = tree[id*2] + tree[id*2+1];
}
node get(int id,int l,int r,int u,int v){
if(v < l || r < u || l > r) return {0,0};
if(u<=l and r<=v) return tree[id];
int mid = (l+r)/2;
return get(2*id,l,mid,u,v) + get(2*id+1,mid+1,r,u,v);
}
int nxt[MLog+1][maxN];
int nhay(int start,int finish){
int u = start;
int res = 0;
for(int i = MLog;i>=0;i--){
if(p[nxt[i][u]].S < finish){
u = nxt[i][u];
res += (1<<i);
}
}
u = nxt[0][u];
res += 1;
return res;
}
int getmax(int i,int j,int finish){
if(p[i].S >= finish) return i; // chi nhay 1 lan
if(p[j].S >= finish) return j;
if(p[i].S <= p[j].S) return j; // nhay xa hon
return i;
}
void ac(){
for(int i = 1;i<=n;i++){
compress.pb(p[i].F);
compress.pb(p[i].S);
// cout << p[i].F << " " << p[i].S << '\n';
}
// cout << '\n' << '\n';
sort(all(compress));
uni(compress);
int sz = compress.size() + 3;
for(int i = n;i>=1;i--){
int cl = lower_bound(all(compress),p[i].F) - compress.begin() + 1;
int cr = lower_bound(all(compress),p[i].S) - compress.begin() + 1; // tim den r+1
nxt[0][i] = get(1,1,sz,cl,cr).id;
up(1,1,sz,cl, {p[i].S, i} );
}
nxt[0][n] = n;
for(int i = 1;i<=MLog;i++){
for(int j = 1;j<=n;j++){
int finish = p[j].F + m;
if(nxt[i-1][j] > n) continue;
// if(i==1 and j == 1){
// cout << nxt[i-1][j] << " " << nxt[i-1][nxt[i-1][j]] << '\n';
// exit(0);
// }
nxt[i][j] = getmax(nxt[i-1][j], nxt[i-1][nxt[i-1][j]], finish);
}
}
int ans = 1e9;
for(int i = 1;i<=n;i++){
int mxid = nxt[MLog][i];
int finish = p[i].F + m;
if(p[mxid].S < finish) continue; // toi da nhay dc -1
// cout << i << " " << nhay(i,finish) + 1<< '\n';
ans = min(ans,nhay(i,finish) + 1);
}
if(ans == 1e9) ans = -1;
cout << ans;
}
pair<int,int> pp[maxN];
int newn = 0;
int mark[maxN];
void tienxuly(){
for(int i = 1;i<=n;i++){
if(mark[i]) continue;
pp[++newn] = p[i];
int j = i;
while(j+1<=n and mark[j+1] == 0 and p[j+1].S <= p[i].S){
mark[j+1] = 1;
++j;
}
}
for(int i = 1;i<=newn;i++){
p[i] = pp[i];
}
n = newn;
}
void solve() {
cin >> n >> m;
for(int i = 1; i<=n; i++) {
cin >> p[i].F >> p[i].S;
if(p[i].F > p[i].S) p[i].S += m;
}
sort(p+1,p+1+n,cmp);
tienxuly();
ac();
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
// freopen("inp.txt","r",stdin);
// freopen("out.txt","w",stdout);
solve();
return 0;
}
