#include <bits/stdc++.h>
using namespace std;
const int N = int(2e5) + 9;
const int LOG = 20;
int up[LOG][N];
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<pair<int, int>> a(n);
for (int i = 0; i < n; i++) {
int s, e;
cin >> s >> e;
if (s > e) {
e += m;
}
a[i] = {s, e};
}
sort(a.begin(), a.end());
vector<int> mx(n);
for (int i = 1; i < n; i++) {
mx[i] = (a[i].second > a[mx[i - 1]].second ? i : mx[i - 1]);
}
for (int i = 0; i < n; i++) {
auto [s, e] = a[i];
int j = upper_bound(a.begin(), a.end(), make_pair(e + 1, -1)) - a.begin() - 1;
up[0][i] = mx[j];
}
for (int j = 1; j < LOG; j++) {
for (int i = 0; i < n; i++) {
up[j][i] = up[j - 1][up[j - 1][i]];
}
}
auto check = [&](int k) {
for (int i = 0; i < n; i++) {
int x = i;
for (int j = 0; j < LOG; j++) {
if ((k - 1) >> j & 1) {
x = up[j][x];
}
}
if (a[x].second - a[i].first >= m) {
return true;
}
}
return false;
};
int low = 1, high = n;
while (low <= high) {
int mid = (low + high) >> 1;
if (check(mid)) {
high = mid - 1;
} else {
low = mid + 1;
}
}
cout << (high + 1 > n ? -1 : high + 1) << '\n';
return 0;
}
