1 #include <iostream>
2 #include <algorithm>
3 #define _for(i,a,b) for(int i = (a);i < b;i ++)
4 #define _rep(i,a,b) for(int i = (a);i > b;i --)
5 #define INF 0x3f3f3f3f
6 typedef long long ll;
7 using namespace std;
8 inline ll read()
9 {
10 ll ans = 0;
11 char ch = getchar(), last = ' ';
12 while(!isdigit(ch)) last = ch, ch = getchar();
13 while(isdigit(ch)) ans = (ans << 1) + (ans << 3) + ch - '0', ch = getchar();
14 if(last == '-') ans = -ans;
15 return ans;
16 }
17 inline void write(ll x)
18 {
19 if(x < 0) x = -x, putchar('-');
20 if(x >= 10) write(x / 10);
21 putchar(x % 10 + '0');
22 }
23 struct section
24 {
25 int l;
26 int r;
27 bool operator < (section b)
28 {
29 if(l != b.l)
30 return l < b.l;
31 return r < b.r;
32 }
33 };
34 int N,T;
35 section a[25003];
36 int main()
37 {
38 N = read(),T = read();
39
40 _for(i,1,N+1)
41 a[i].l = read(),a[i].r = read();
42
43 sort(a+1,a+N+1);
44
45 int l = 0,i = 0;
46 int rnt = 0;
47 while(l < T)
48 {
49 int maxr = -1;
50 while(a[++i].l <= l+1 && i < N+1)
51 maxr = max(maxr,a[i].r);
52 if(i > N+1)
53 break;
54 if(maxr==-1) {printf("-1\n");return 0;}
55 rnt ++;
56 i --;
57 l = maxr;
58 }
59 printf("%d\n",rnt);
60 return 0;
61 }
