#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#include <map>
int x, max_coord;
std::vector<std::pair<int,int>> arr;
std::vector<std::vector<int>> next;
void read_data() {
std::cin >> x >> max_coord;
bool has_start = 0, has_finish = 0;
for (int i = 0, a, b; i < x; i++) {
std::cin >> a >> b;
if (a <= b) {
if (a == 0) {
has_start = 1;
}
if (b == max_coord-1) {
has_finish = 1;
}
}
else {
has_start = 1;
has_finish = 1;
}
a = std::max(0, a-1);
arr.emplace_back(a,b);
}
if (!has_start || !has_finish) {
std::cout << "-1\n";
exit(0);
}
}
void normalize_data() {
std::map<int,int> map;
for (int i = 0; i < x; i++) {
if (arr[i].first+1 <= arr[i].second) {
map[arr[i].first] = 0;
map[arr[i].second] = 0;
}
else {
map[0] = 0;
map[max_coord-1] = 0;
map[arr[i].first] = 0;
map[arr[i].second] = 0;
}
}
max_coord = 0;
for (auto& i : map) {
i.second = max_coord++;
}
for (int i = 0; i < x; i++) {
arr[i].first = map[arr[i].first];
arr[i].second = map[arr[i].second];
//std::cout << arr[i].first << " " << arr[i].second << "\n";
}
}
void build_jump_table() {
next.assign(32-__builtin_clz(max_coord), std::vector<int>(max_coord, 0));
std::vector<int> tmp(max_coord, 0);
for (int i = 0; i < x; i++) {
if (arr[i].first+1 <= arr[i].second) {
tmp[arr[i].first] = std::max(tmp[arr[i].first], arr[i].second);
}
else {
tmp[0] = std::max(tmp[0], arr[i].second);
tmp[arr[i].first] = std::max(tmp[arr[i].first], max_coord-1);
}
}
int pfx_max = 0;
for (int i = 0; i < max_coord; i++) {
pfx_max = std::max(pfx_max, tmp[i]);
next[0][i] = std::max(pfx_max, i);
//std::cout << tmp[i] << " ";
//std::cout << next[0][i] << " ";
}
//std::cout << "\n";
for (int l = 1; l < next.size(); l++) {
for (int i = 0; i < max_coord; i++) {
next[l][i] = next[l-1][next[l-1][i]];
}
}
}
int try_solve(int st, int fi) {
int ret = 0;
int p = st;
for (int step = next.size()-1; step >= 0; step--) {
if (next[step][p] < fi) {
ret += (1<<step);
p = next[step][p];
}
}
return ((next[0][p]>=fi) ? ret + (p < fi) : 0x3f3f3f3f);
}
void solve() {
int ret = 0x3f3f3f3f;
ret = std::min(ret, try_solve(0, max_coord-1));
for (int i = 0; i < x; i++) {
if (arr[i].first+1 > arr[i].second) {
ret = std::min(ret, 1 + try_solve(arr[i].second-1, arr[i].first));
}
}
std::cout << ((ret!=0x3f3f3f3f) ? ret : -1) << "\n";
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(NULL);
std::cout.tie(NULL);
read_data();
normalize_data();
build_jump_table();
solve();
}
