#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
#define FF first
#define SS second
#define all(a) a.begin(), a.end()
#define mod (ll)(1000000007)
const int N = 1 << 15;
array<int, 2> bad = {(int)1e5 + 1, (int)1e5 + 1};
vector<array<int, 2>> S(1e4 + 1, bad);
void clear_them() {
S.clear();
S.resize(1e4 + 1, bad);
}
void update(int i, int idx, int val) {
S[idx][i] = val;
}
int get(int i, int id, int u, int v, int l, int r) {
int mn = 1e5 + 1;
for (int j = u; j <= v; j++) {
mn = min(mn, S[j][i]);
}
return mn;
}
int main() {
ios_base::sync_with_stdio(0);cin.tie(0);
int n, m;
cin >> n >> m;
vector<int> All;
All.reserve(2 * n);
vector<array<int, 2>> A(n);
for (int i = 0; i < n; i++) {
cin >> A[i][0] >> A[i][1];
All.push_back(A[i][0]);
All.push_back(A[i][1]);
}
sort(all(All));
map<int, int> new_;
int cnt = 0;
for (int i = 0; i < All.size(); i++) {
if (!i || All[i] != All[i - 1]) {
new_[All[i]] = cnt++;
}
}
int sz = cnt;
for (int i = 0; i < n; i++) {
A[i][0] = new_[A[i][0]], A[i][1] = new_[A[i][1]];
}
int ans = n + 1;
for (int k = 0; k < All.size(); k++) {
int cur = new_[All[k]];
vector<vector<int>> Events(sz);
for (int j = 0; j < n; j++) {
Events[A[j][0]].push_back(j);
Events[A[j][1]].push_back(j);
}
vector<int> Prf(sz + 1, n + 1), Suf(sz + 1, n + 1);
Prf[cur] = 0;
update(0, cur, Prf[cur]);
for (int i = cur + 1; i % sz != cur; i++) {
i %= sz;
for (auto j : Events[i]) {
if (A[j][0] < A[j][1]) {
if (i != A[j][1] || (cur > A[j][0] && cur < A[j][1])) {
continue;
}
Prf[i] = min(Prf[i], get(0, 1, A[j][0], A[j][1], 0, N - 1) + 1);
}
else {
if (i != A[j][1] || cur > A[j][0] || cur < A[j][1]) {
continue;
}
Prf[i] = min(Prf[i], min(get(0, 1, A[j][0], sz - 1, 0, N - 1), get(0, 1, 0, A[j][1], 0, N - 1)) + 1);
}
}
update(0, i, Prf[i]);
}
{
int i = cur;
for (auto j : Events[i]) {
if (A[j][0] < A[j][1]) {
if (i != A[j][1] || (cur > A[j][0] && cur < A[j][1])) {
continue;
}
Prf[sz] = min(Prf[sz], get(0, 1, A[j][0], A[j][1] - 1, 0, N - 1) + 1);
}
else {
if (i != A[j][1] || cur > A[j][0] || cur < A[j][1]) {
continue;
}
Prf[sz] = min(Prf[sz], min(get(0, 1, A[j][0], sz - 1, 0, N - 1), get(0, 1, 0, A[j][1] - 1, 0, N - 1)) + 1);
}
}
}
Suf[cur] = 0;
update(1, cur, Suf[cur]);
for (int i = cur - 1; (i + sz) % sz != cur; i--) {
i += sz;
i %= sz;
for (auto j : Events[i]) {
if (A[j][0] < A[j][1]) {
if (i != A[j][0] || (cur > A[j][0] && cur < A[j][1])) {
continue;
}
Suf[i] = min(Suf[i], get(1, 1, A[j][0], A[j][1], 0, N - 1) + 1);
}
else {
if (i != A[j][0] || cur > A[j][0] || cur < A[j][1]) {
continue;
}
Suf[i] = min(Suf[i], min(get(1, 1, A[j][0], sz - 1, 0, N - 1), get(1, 1, 0, A[j][1], 0, N - 1)) + 1);
}
}
update(1, i, Suf[i]);
}
{
int i = cur;
for (auto j : Events[i]) {
if (A[j][0] < A[j][1]) {
if (i != A[j][0] || (cur > A[j][0] && cur < A[j][1])) {
continue;
}
Suf[sz] = min(Suf[sz], get(1, 1, A[j][0] + 1, A[j][1], 0, N - 1) + 1);
}
else {
if (i != A[j][0] || cur > A[j][0] || cur < A[j][1]) {
continue;
}
Suf[sz] = min(Suf[sz], min(get(1, 1, A[j][0] + 1, sz - 1, 0, N - 1), get(1, 1, 0, A[j][1], 0, N - 1)) + 1);
}
}
}
clear_them();
Prf[(cur - 1 + sz) % sz] = min(Prf[(cur - 1 + sz) % sz], Prf[sz]);
for (int i = cur - 2; (i + sz) % sz != cur; i--) {
i += sz;
i %= sz;
Prf[i] = min(Prf[i], Prf[(i + 1) % sz]);
}
Suf[(cur + 1) % sz] = min(Suf[(cur + 1) % sz], Suf[sz]);
for (int i = cur + 2; i % sz != cur; i++) {
i %= sz;
Suf[i] = min(Suf[i], Suf[(i - 1 + sz) % sz]);
}
for (int i = 0; i < sz; i++) {
if (i == cur) {
continue;
}
ans = min(ans, Prf[i] + Suf[i]);
}
}
if (ans == n + 1) {
ans = -1;
}
cout << ans;
}
