#include<iostream>
#include<stack>
#include<map>
#include<vector>
#include<string>
#include<cassert>
#include<unordered_map>
#include <queue>
#include <cstdint>
#include<cstring>
#include<limits.h>
#include<cmath>
#include<set>
#include<algorithm>
#include <iomanip>
#include<numeric>
#include<bitset>
using namespace std;
#define ll long long
#define f first
#define s second
#define pii pair<int,int>
#define ppii pair<int,pii>
#define vi vector<int>
#define pb push_back
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define F(n) for(int i=0;i<n;i++)
#define lb lower_bound
#define ub upper_bound
#define fastio ios::sync_with_stdio(false);cin.tie(NULL);
#pragma GCC optimize ("03,unroll-lopps")
#define int long long
using namespace std;
const int mod=1e9+7,mxn=1e6+5,inf=1e18,minf=-1e18,lg=30;
//#undef int
int n,k,m;
void setIO(string name){
ios_base::sync_with_stdio(0); cin.tie(0);
freopen((name+".in").c_str(),"r",stdin);
freopen((name+".out").c_str(),"w",stdout);
}
int sz=0;
struct seg2{
pii v[2*mxn+10];
void init(){for(int i=0;i<=2*sz;i++)v[i]={minf,minf};}
void update(int pos,pii val){
pos+=sz;
v[pos]=max(v[pos],val);
for(int i=pos;i>0;i>>=1)v[i>>1]=max(v[i],v[i^1]);
}
pii qry(int l,int r){
pii ans={minf,minf};
for(l+=sz,r+=sz;l<=r;l>>=1,r>>=1){
if(l&1)ans=max(ans,v[l++]);
if(!(r&1))ans=max(ans,v[r--]);
}
return ans;
}
}t2;
vector<int>adj[mxn+10];
int ans=inf;
vector<pii>v,v2;
vector<int>point;
int up[mxn+10][lg+1],up2[mxn+10],bruh[mxn+10];
int32_t main(){
fastio
cin>>n>>m;
v.resize(n);
for(int i=0;i<n;i++){
cin>>v[i].f>>v[i].s;
if(v[i].f>v[i].s){
point.pb(v[i].f);
point.pb(v[i].s+m+1);
}
else{
point.pb(v[i].f);
point.pb(v[i].s);
point.pb(v[i].f+m+1);
point.pb(v[i].s+m+1);
}
}
sort(all(point));
point.erase(unique(all(point)),point.end());
int id=0;
sz=point.size();
t2.init();
for(auto &i:v){
v2.pb({i.f,i.s});
if(i.f<i.s){
t2.update(lb(all(point),i.f)-point.begin(),{lb(all(point),i.s)-point.begin(),id});
t2.update(lb(all(point),i.f+m+1)-point.begin(),{lb(all(point),i.s+m+1)-point.begin(),id});
i.f=lb(all(point),i.f)-point.begin(),i.s=lb(all(point),i.s)-point.begin();
}
else{
t2.update(lb(all(point),i.f)-point.begin(),{lb(all(point),i.s+m+1)-point.begin(),id});
i.f=lb(all(point),i.f)-point.begin(),i.s=lb(all(point),i.s+m+1)-point.begin();
}
id++;
}
for(int i=0;i<n;i++){
if(v2[i].f<v2[i].s){
int go=t2.qry(v[i].f,v[i].s).s;
if(go!=minf&&go!=i)up[i][0]=go;
else up[i][0]=i,bruh[i]=1;
}
else{
int go=t2.qry(v[i].f,v[i].s).s;
up[i][0]=i;
if(go==i)bruh[i]=1;
up2[i]=go;
}
}
for(int i=1;i<=lg;i++)for(int j=0;j<n;j++)up[j][i]=up[up[j][i-1]][i-1];
for(int i=0;i<n;i++){
int x=up[i][lg],cnt=1,cur=i;
if(bruh[cur])continue;
for(int j=lg;j>=0;j--)if(up[cur][j]!=x)cur=up[cur][j],cnt+=(1LL<<j);
if(cur!=x)cur=up[cur][0],cnt++;
if(bruh[cur])continue;
while(v2[cur].f>v2[cur].s){
cur=up2[cur];
cnt++;
if(bruh[cur])break;
if(v2[cur].s>=v2[i].f)break;
}
x=up[cur][lg];
if(bruh[cur])continue;
if(v2[cur].s>=v2[i].f){
ans=min(ans,cnt);
continue;
}
for(int j=lg;j>=0;j--)if(up[cur][j]!=x&&v2[up[cur][j]].s<v2[i].f)cur=up[cur][j],cnt+=(1LL<<j);
if(bruh[cur])continue;
cur=up[cur][0];
if(bruh[cur])continue;
cnt++;
if(v2[cur].s>=v2[i].f||cur==x)ans=min(ans,cnt);
}
if(ans>=inf)cout<<-1;
else cout<<ans;
}
/*
12
58
66
68
92
125
150
175
223
269
288
291
3
8 100
10 30
30 50
50 70
40 60
60 80
50 70
80 100
100 20
4 100
0 30
30 70
70 100
60 20
1 100
30 40
*/
