#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <iomanip>
#include <array>
#include <string>
#include <algorithm>
#include <cmath>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <bitset>
#include <list>
#include <iterator>
#include <numeric>
#include <complex>
#include <utility>
#include <random>
#include <cassert>
#include <fstream>
using namespace std;
mt19937 rnd(time(nullptr));
/* -------------------- Typedefs -------------------- */
typedef int itn;
typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef float fl;
typedef long double ld;
/* -------------------- Usings -------------------- */
using vi = vector<int>;
using vll = vector<ll>;
using mii = map<int, int>;
using mll = map<ll, ll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
/* -------------------- Defines -------------------- */
#define ff first
#define ss second
#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
#define mpr make_pair
#define yes cout<<"Yes\n"
#define no cout<<"No\n"
#define all(x) (x).begin(), (x).end()
#define USACO freopen("feast.in", "r", stdin); freopen("feast.out", "w", stdout);
/* -------------------- Constants -------------------- */
const int dx[8] = { -1, 0, 1, 0, -1, -1, 1, 1 };
const int dy[8] = { 0, -1, 0, 1, -1, 1, -1, 1 };
const int MAX = int(1e9 + 5);
const ll MAXL = ll(1e18) + 5ll;
const ll MOD = ll(1000000007);
const ll MOD2 = ll(998244353);
/* -------------------- Functions -------------------- */
void fastio() {
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
}
void precision(int x) {
cout.setf(ios::fixed | ios::showpoint);
cout.precision(x);
}
ll gcd(ll a, ll b) {
if (a == 0 || b == 0) return(max(a, b));
while (b) {
a %= b;
swap(a, b);
}
return a;
}
ll lcm(ll a, ll b) {
return a / gcd(a, b) * b;
}
ll range_sum(ll a, ll b) {
if (a > b) return 0ll;
ll dif = a - 1, cnt = b - a + 1;
ll ans = ((b - a + 1) * (b - a + 2)) / 2;
ans += ((b - a + 1) * dif);
return ans;
}
string dec_to_bin(ll a) {
string s = "";
for (ll i = a; i > 0; ) {
ll k = i % 2;
i /= 2;
char c = k + 48;
s += c;
}
if (a == 0) {
s = "0";
}
reverse(all(s));
return s;
}
ll bin_to_dec(string s) {
ll num = 0;
for (int i = 0; i < s.size(); i++) {
num *= 2ll;
num += (s[i] - '0');
}
return num;
}
ll factorial_by_mod(ll n, ll mod) {
ll ans = 1;
ll num;
for (ll i = 1; i <= n; ++i) {
num = i % mod;
ans *= num;
ans %= mod;
}
return ans;
}
bool isPrime(ll a) {
if (a == 1) return false;
for (ll i = 2; i * i <= a; i++) {
if (a % i == 0) return false;
}
return true;
}
ll binpow(ll a, ll b) {
if (!a) return 0;
ll ans = 1;
while (b) {
if (b & 1) {
ans *= a;
}
b >>= 1;
a *= a;
}
return ans;
}
ll binpow_by_mod(ll a, ll b, ll mod) {
if (!a) return 0;
ll ans = 1;
while (b) {
if (b & 1) {
ans *= a;
ans %= mod;
}
b >>= 1;
a *= a;
a %= mod;
}
return ans;
}
/* -------------------- Solution -------------------- */
const int N = 400005, M = 25;
int t[N], id_rev[N], till[N], cayr[N], up[N][M];
pii a[N];
int n, m, k, lg;
set<int> st;
unordered_map<int, int> id;
void slv() {
cin >> n >> k;
lg = log2(n);
vi v;
for (int i = 1; i <= n; ++i) {
cin >> a[i].ff >> a[i].ss;
if (a[i].ss == 0 || a[i].ss < a[i].ff) {
v.pub(i);
}
st.insert(a[i].ff);
st.insert(a[i].ss);
}
for (auto elem : st) {
id[elem] = ++m;
id_rev[m] = elem;
}
for (int i = 1; i <= n; ++i) {
a[i].ff = id[a[i].ff];
a[i].ss = id[a[i].ss];
cayr[a[i].ff] = a[i].ss;
}
for (int i = 1; i <= m; ++i) {
till[i] = max(till[i - 1], cayr[i]);
}
for (int i = m; i >= 1; --i) {
up[i][0] = till[i];
for (int l = 1; l <= lg; ++l) {
up[i][l] = up[up[i][l - 1]][l - 1];
}
}
int ans = MAX;
for (auto elem : v) {
int s = a[elem].ss, e = a[elem].ff;
int answ = 0;
for (int l = lg; l >= 0; --l) {
if (up[s][l] == 0) continue;
if (l != 0 && up[s][l - 1] >= e) continue;
s = up[s][l];
answ += (1 << l);
}
if (s < e) continue;
ans = min(ans, answ);
}
cout << (ans == MAX ? -1 : ans);
}
void cs() {
int tstc = 1;
//cin >> tstc;
while (tstc--) {
slv();
}
}
void precalc() {
return;
}
int main() {
fastio();
precalc();
//precision(0);
cs();
return 0;
}
