#include<bits/stdc++.h>
typedef long long ll;
#define pii pair<ll, ll>
#define fi first
#define se second
#define endl '\n'
#define TASK ""
#define N 500006
#define LOG 19
using namespace std;
const ll inf = 1e18;
bool ghuy4g;
ll n, m, cur, sz;
vector<ll> ns;
pii p[N];
vector<pii> st;
ll par[N][LOG + 2];
void pre() {
sort(p + 1, p + 1 + cur);
/*cout << "sz " << sz << endl;
for (int i = 1; i <= cur; i ++) {
cout << p[i].fi << " " << p[i].se << endl;
}*/
ll mx = 0;
ll id = 1;
for (int i = 1; i <= sz; i ++) {
while (id <= cur && p[id].fi <= i) {
mx = max(mx, p[id].se);
id ++ ;
}
par[i][0] = mx;
//cout << " i " << i << " " << par[i][0] << endl;
}
par[sz + 1][0] = sz + 1;
for (int j = 1; j <= LOG; j ++) {
for (int i = 1; i <= sz; i ++) {
ll p = par[i][j - 1];
par[i][j] = par[p][j - 1];
}
}
}
void solve() {
ll ans = inf;
for (auto it : st) {
if (it.fi == 1) {
ll cur = it.se;
ll res = 0;
for (int j = LOG; j >= 0; j --) {
if (par[cur][j] < sz) {
cur = par[cur][j];
res += (1 << j);
}
}
cur = par[cur][0];
res ++ ;
if (cur >= sz) {
ans = min(ans, res + 1);
}
}
else {
ll cur = it.se;
ll res = 0;
for (int j = LOG; j >= 0; j --) {
if (par[cur][j] < it.fi) {
cur = par[cur][j];
res += (1 << j);
}
}
cur = par[cur][0];
res ++ ;
if (cur >= it.fi) {
ans = min(ans, res + 1);
}
}
}
if (ans == inf) {
ans = -1;
}
cout << ans << endl;
}
bool klinh;
signed main() {
//freopen("sort.inp", "r", stdin);
//freopen("sort.out", "w", stdout);
//srand(time(0));
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n >> m;
ns.push_back(m);
for (int i = 1; i <= n; i ++) {
ll u, v;
cin >> u >> v;
if (u <= v && u > 0) {
p[++ cur] = {u, v};
}
else if (v == 0) {
v = m;
p[++ cur] = {u, v};
}
else {
st.push_back({u, v});
}
//cout << " u v " << u << " " << v << endl;
ns.push_back(u);
ns.push_back(v);
}
sort(ns.begin(), ns.end());
ns.resize(unique(ns.begin(), ns.end()) - ns.begin());
sz = ns.size();
/*for (auto it : ns) {
cout << it << " ";
}
cout << endl;*/
for (int i = 1; i <= cur; i ++) {
p[i].fi = lower_bound(ns.begin(), ns.end(), p[i].fi) - ns.begin() + 1;
p[i].se = lower_bound(ns.begin(), ns.end(), p[i].se) - ns.begin() + 1;
}
for (auto &it : st) {
it.fi = lower_bound(ns.begin(), ns.end(), it.fi) - ns.begin() + 1;
it.se = lower_bound(ns.begin(), ns.end(), it.se) - ns.begin() + 1;
//cout << " it " << it.fi << " " << it.se << endl;
}
pre();
solve();
cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
cerr << fabs(&klinh - &ghuy4g) / 1048576.0;
}
