1 #include<iostream>
 2 #include<algorithm>
 3 using namespace std;
 4 struct P
 5 {
 6     long int first;
 7     long int second;
 8 };
 9 int cmp(P x,P y)
10 {
11     if(x.first==y.first)
12     return x.second<y.second;
13     return x.first<y.first;
14 }
15 int main()
16 {
17     long int n,m;
18     cin>>n>>m;
19     P p[25005];
20     long int i,j;
21     for(i=0;i<n;i++)
22     cin>>p[i].first>>p[i].second;
23     p[n].first=99999;
24     sort(p,p+n,cmp);
25     for(i=0;i<n;i++)
26         if(p[i].second==m)break;
27     if(p[0].first!=1)cout<<-1<<endl;
28     else if(i==n)cout<<-1<<endl;
29     else
30     {
31         long int count=1;
32         long int pos;
33         P *q=p;
34         while(q->first==1)q++;
35         q--;
36         pos=q->second;
37         long int posi;
38         bool f=0;
39         while(pos!=m)
40         {
41             q++;
42            posi=pos;
43             while(q->first<=pos+1&&posi<m)
44             {
45                 if(q->second>posi)posi=q->second;
46                 q++;
47             }
48             if(q->first>posi+1&&posi!=m){f=1;break;}
49             q--;
50             pos=posi;
51             count++;
52         }
53         if(f==1)cout<<-1<<endl;
54         else
55         cout<<count<<endl;
56     }
57     return 0;
58 }