#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];
int nxt[mxN + 1][21];
vector<int> normal;
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].first);
normal.emplace_back(se[i].second);
}
sort(normal.begin(), normal.end());
normal.erase(unique(normal.begin(), normal.end()), normal.end());
sort(se, se + N);
priority_queue<pair<int,int>> pq;
int id = 0, r = 0;
for (int i = 0; i < (int) normal.size(); i++) {
for (; id < N && se[id].first == normal[i]; id++) {
pq.push({-se[id].second, id});
if (se[id].second > se[r].second) {
r = id;
}
}
if (!pq.empty()) {
int tmp = r;
for (; !pq.empty() && -pq.top().first == normal[i]; pq.pop()) {
nxt[pq.top().second][0] = tmp;
}
}
}
for (int j = 1; j < 20; j++) {
for (int i = 0; i < N; i++) {
nxt[i][j] = nxt[nxt[i][j - 1]][j - 1];
}
}
int ans = N + 1;
for (int i = 0; i < N; i++) {
int now = i, cnt = 1;
for (int j = 19; j >= 0; j--) {
if (se[nxt[now][j]].second < se[i].first + M) {
now = nxt[now][j];
cnt += (1 << j);
}
}
now = nxt[now][0];
cnt++;
if (se[now].second >= se[i].first + M) {
ans = min(ans, cnt);
}
}
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;
}
