#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(0);
int n, m;
cin >> n >> m;
vector<int> a(n);
vector<int> b(n);
for (int i = 0; i < n; i++) {
cin >> a[i] >> b[i];
if (a[i] > b[i]) {
b[i] += m;
}
}
vector<pair<int, int>> ev;
for (int i = 0; i < n; i++) {
ev.emplace_back(a[i], ~i);
ev.emplace_back(b[i], i);
}
sort(ev.begin(), ev.end());
set<pair<int, int>> st;
const int L = 20;
vector<vector<int>> jump(n, vector<int>(L));
for (auto& p : ev) {
int i = p.second;
if (i >= 0) {
jump[i][0] = prev(st.end())->second;
st.erase({b[i], i});
} else {
i = ~i;
st.insert({b[i], i});
}
}
for (int j = 1; j < L; j++) {
for (int i = 0; i < n; i++) {
jump[i][j] = jump[jump[i][j - 1]][j - 1];
}
}
int res = n + 1;
for (int i = 0; i < n; i++) {
int idx = i;
int total = 1;
for (int j = L - 1; j >= 0; j--) {
if (b[jump[idx][j]] < a[i] + m) {
idx = jump[idx][j];
total += (1 << j);
}
}
res = min(res, total + 1);
}
if (res > n) {
cout << -1 << '\n';
} else {
cout << res << '\n';
}
return 0;
}
