/*
In the name of Allah
made by: Ahmed_Solyman
*/
#include <bits/stdc++.h>
#include <ext/rope>
using namespace std;
using namespace __gnu_cxx;
#pragma GCC optimize("-Ofast")
#pragma GCC optimize("-O1")
//-------------------------------------------------------------//
typedef long long ll;
typedef unsigned long long ull;
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define PI acos(-1)
#define lb lower_bound
#define ub upper_bound
#define endl '\n'
#define all(v) v.begin(),v.end()
#define allr(v) v.rbegin(),v.rend()
#define sum_to(n) (n*(n+1))/2
#define pb push_back
#define pf push_front
#define fil(arr,x) memset(arr,x,sizeof(arr))
#define REP(i,a,b) for (int i=a;i<=b;i++)
#define F first
#define S second
#define MP make_pair
int dx[8]={0,1,0,-1,1,1,-1,-1};
int dy[8]={1,0,-1,0,1,-1,-1,1};
//-------------------------------------------------------------//
ll lcm(ll a,ll b)
{
return (max(a,b)/__gcd(a,b))*min(a,b);
}
void person_bool(bool x) {
cout<<(x?"YES":"NO")<<endl;
}
int solve(int n,int m,vector<int>l,vector<int>r,int s,int e) {
map<int,int>mp;
for (int i=0;i<n;i++) {
l[i]=max(l[i],s);
r[i]=min(r[i],e);
if (l[i]>=r[i])continue;
mp[l[i]]=max(mp[l[i]],r[i]);
}
vector<pair<int,int>>vec;
for (auto i:mp)
vec.push_back(i);
vec.push_back({e,e});
int R=s;
int mx=0;
int ans=0;
for (auto i:vec) {
if (R==e)break;
if (i.first>R) {
if (mx>=i.first) {
ans++;
R=mx;
}
else {
return -1;
}
}
mx=max(mx,i.second);
}
return ans;
}
int main() {
fast
int n,m;
cin>>n>>m;
vector<int>l(n),r(n);
for (int i=0;i<n;i++)
cin>>l[i]>>r[i];
int L=0,R=m;
for (int i=0;i<n;i++)
if (r[i]<l[i]) {
L=max(L,r[i]);
R=min(R,l[i]);
}
if (R==m) {
cout<<-1<<endl;
return 0;
}
bool e=0;
int x=m,y=0;
for (int i=0;i<n;i++) {
e|=(l[i]==R && r[i]==L);
if (r[i]==L)x=min(x,l[i]);
if (l[i]==R)y=max(y,r[i]);
}
if (e) {
int ans=solve(n,m,l,r,L,R);
if (ans==-1)cout<<ans<<endl;
else cout<<ans+1<<endl;
}
else {
int ans=(L<R?solve(n,m,l,r,L,R):0);
if (ans==-1)cout<<ans<<endl;
else {
int x=ans+2;
int ans2=solve(n,m,l,r,L,x);
int ans3=solve(n,m,l,r,y,R);
if (~ans2)x=min(x,ans2+1);
if (~ans3)x=min(x,ans3+1);
cout<<x<<endl;
}
}
}
