#include <bits/stdc++.h>
using namespace std;
const int M = 8e5 + 1, lg = 20;
int maxx[M][lg],ind[M][lg],nxt[M][lg];
int get(int l,int r)
{
int b=31-__builtin_clz(r-l);
int mx=max(maxx[l][b],maxx[r-(1<<b)][b]);
if (mx==maxx[l][b])
return ind[l][b];
return ind[r-(1<<b)][b];
}
int main()
{
int n,m;
cin>>n>>m;
set<pair<int,int>> se,se1;
vector<pair<int,int>> v;
set<int> vl;
for (int i=0;i<2*n;i++)
for (int p=0;p<lg;p++)
ind[i][p]=-1;
int s[n],e[n];
for (int i=0;i<n;i++)
{
cin>>s[i]>>e[i];
vl.insert(s[i]),vl.insert(e[i]);
}
map<int,int> id;
for (int i:vl)
id[i]=id.size();
int k=id.size();
for (int i=0;i<n;i++)
{
s[i]=id[s[i]],e[i]=id[e[i]];
if (s[i]<e[i])
v.push_back({s[i],e[i]}),v.push_back({s[i]+k,e[i]+k});
else
v.push_back({s[i],e[i]+k});
}
sort(v.begin(),v.end());
for (int i=0;i<n;i++)
{
if (s[i]<e[i])
{
maxx[s[i]][0]=max(maxx[s[i]][0],e[i]);
maxx[s[i]+k][0]=max(maxx[s[i]+k][0],e[i]+k);
}
else
maxx[s[i]][0]=max(maxx[s[i]][0],e[i]+k);
}
for (int i=0;i<2*k;i++)
{
ind[i][0]=-1;
if (maxx[i][0])
ind[i][0]=lower_bound(v.begin(),v.end(),make_pair(i,maxx[i][0]))-begin(v);
}
for (int p=1;p<lg;p++)
for (int i=0;i+(1<<p)<=4*n;i++)
{
maxx[i][p]=max(maxx[i][p-1],maxx[i+(1<<p-1)][p-1]),ind[i][p]=ind[i][p-1];
if (maxx[i][p]!=maxx[i][p-1])
ind[i][p]=ind[i+(1<<p-1)][p-1];
}
for (int i=0;i<v.size();i++)
{
nxt[i][0]=get(v[i].first,v[i].second+1);
if (nxt[i][0]==i)
nxt[i][0]=-1;
}
for (int p=1;p<lg;p++)
for (int i=0;i<v.size();i++)
{
if (nxt[i][p-1]==-1)
nxt[i][p]=-1;
else
nxt[i][p]=nxt[nxt[i][p-1]][p-1];
}
int ans=n+1;
for (int i=0;i<v.size();i++)
{
if (v[i].first>=k) continue;
int val=1,x=i;
for (int p=lg-1;p>=0;p--)
if (nxt[x][p]!=-1 && v[nxt[x][p]].second<v[i].first+k)
val+=(1<<p),x=nxt[x][p];
if (nxt[x][0]!=-1 && v[nxt[x][0]].second>=v[i].first+k)
ans=min(ans,val+1);
}
if (ans==n+1)
ans=-1;
cout<<ans<<endl;
return 0;
}
