#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
constexpr int mxN = 200'000;
int N, M;
pair<int,int> se[mxN + 1];
vector<int> normal;
i64 dp[3 * mxN + 5];
int getNorm(int x) {
int lo = 0, hi = (int) normal.size() - 1;
while (lo <= hi) {
int mid = lo + (hi - lo) / 2;
if (normal[mid] == x) return mid;
else if (normal[mid] < x) lo = mid + 1;
else hi = mid - 1;
}
return -1;
}
void solve() {
cin >> N >> M;
for (int i = 0; i < N; i++) {
cin >> se[i].first >> se[i].second;
if (se[i].second < se[i].first) {
se[i].second += M;
normal.emplace_back(se[i].second - M);
}
normal.emplace_back(se[i].first);
normal.emplace_back(se[i].second);
}
sort(normal.begin(), normal.end());
normal.erase(unique(normal.begin(), normal.end()), normal.end());
for (int i = 0; i < N; i++) {
se[i].first = getNorm(se[i].first);
se[i].second = getNorm(se[i].second);
}
sort(se, se + N);
i64 ans = 1LL * (N + 1) * (N + 1);
for (int i = 0; i < (int) normal.size(); i++) {
dp[i] = 1LL * i * (N + 1);
}
int id = 0;
priority_queue<pair<int,int>> pq; // rl
for (int i = 0; i < (int) normal.size(); i++) {
for (; id < N && se[id].first == i; id++) {
pq.push({-se[id].second, -se[id].first});
}
if (pq.empty()) {
cout << "-1\n";
return;
}
dp[i] = min(dp[i], dp[-pq.top().second] + 1);
for (; !pq.empty() && -pq.top().first == i; pq.pop()) {
int r = -pq.top().first;
if (normal[r] >= M) {
int l = -pq.top().second;
ans = min(ans, 1 + dp[l] - dp[getNorm(r - M)]);
}
}
}
if (ans > N) ans = -1;
cout << ans << '\n';
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int tc = 1;
//cin >> tc;
while (tc--) {
solve();
}
return 0;
}
