#include<bits/stdc++.h>
using namespace std;
int n, m, e[200001], s[200001], ma=0, ans=1e9;
vector<pair<int, int>> now;
bool cmp(pair<int, int> a, pair<int, int> b){
if(a.first==b.first)return a.second>b.second;
return a.first<b.first;
}
vector<pair<int, int>> chosenone;
int main(){
ios::sync_with_stdio(0);cin.tie(nullptr);
cin>>n>>m;
for(int i=1;i<=n;i++){
cin>>s[i]>>e[i];
ma=max(ma, e[i]);
if(s[i]<=e[i])now.push_back({s[i], e[i]});
}
sort(now.begin(), now.end(), cmp);
int cnt=2;
int nxt=now[0].second, R=now[0].second, L=now[0].first;
chosenone.push_back({L, R});
for(int i=1;i<now.size();i++){
if(nxt+1<now[i].first){
cnt++;
nxt=R;
chosenone.push_back({L, R});
if(R==ma)break;
}
if(R<now[i].second){
R=now[i].second;
L=now[i].first;
}
}
if(chosenone.back().second!=ma)chosenone.push_back({L, R});
chosenone.erase(unique(chosenone.begin(), chosenone.end()), chosenone.end());
for(int i=1;i<chosenone.size();i++){
if(chosenone[i].first>chosenone[i-1].second){
cout<<-1;
return 0;
}
}
//for(auto[u, v] : chosenone)cout<<u<<" "<<v<<"\n";
for(int i=1;i<=n;i++){
if(s[i]>e[i]){
int l=0, r=chosenone.size()-1, mid, vtst=-1;
while(l<=r){
mid=(l+r)/2;
if(chosenone[mid].second>=s[i]){
vtst=mid;
r=mid-1;
}
else l=mid+1;
}
l=0, r=chosenone.size()-1;
int vten=-1;
while(l<=r){
mid=(l+r)/2;
if(chosenone[mid].first<=e[i]){
vten=mid;
l=mid+1;
}
else r=mid-1;
}
if(vten!=-1 and vtst!=-1){
vtst++;
ans=min(ans, int(chosenone.size()-(chosenone.size()-vtst)-vten)+1);
}
}
}
if(ans==1e9)cout<<-1;
else cout<<ans;
return 0;
}
