#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cmath>
#include<set>
#include<map>
#include<queue>
#include<stack>
#include<unordered_map>
#include<unordered_set>
using namespace std;
using ll = long long;
ll mod = 998244353;
ll gcd(ll a, ll b) {
if (b == 0)return a;
else return gcd(b, a % b);
}
vector<pair<int, int>>v;
vector<pair<int, int>>seg;
void build(int l, int r, int u) {
if (l == r) {
seg[u] = { v[l].second,l };
return;
}
int mid = (l + r) / 2;
build(l, mid, 2 * u + 1);
build(mid+1, r, 2 * u + 2);
seg[u] = max(seg[2 * u + 1], seg[2 * u + 2]);
}
pair<int,int> get(int l, int r, int u,int lx,int rx) {
if (l >=lx&&r<=rx) {
return seg[u];
}
if (l > rx || r < lx) {
return { -1,-1 };
}
int mid = (l + r) / 2;
return max({ get(l, mid, 2 * u + 1,lx,rx),get(mid + 1, r, 2 * u + 2,lx,rx) });
}
void solve() {
int n, m; cin >> n >> m;
v=vector<pair<int,int>>(n);
int f = 1;
for (int i = 0; i < n; i++) {
cin >> v[i].first >> v[i].second;
if (v[i].first > v[i].second) {
v[i].second += m;
}
if (v[i].second - v[i].first + 1 >= m)f = 0;
}
if (f == 0) {
cout << 1 << endl;
return;
}
sort(v.begin(), v.end());
int s = 1;
while (s < n)s <<= 1;
seg = vector<pair<int, int>>(2 * s - 1);
build(0, s - 1, 0);
vector<vector<int>>up(n, vector<int>(22));
for (int i = 0; i < n; i++) {
pair<int, int>p;
p.first = v[i].second+1;
p.second = -1;
int ind = lower_bound(v.begin(), v.end(), p) - v.begin() - 1;
int bro = get(0, s - 1, 0, i, ind).second;
up[i][0] = bro;
}
for (int i = n - 1; i >= 0; i--) {
for (int j = 1; j <= 20; j++) {
up[i][j] = up[up[i][j - 1]][j - 1];
}
}
int ans = 1e9;
for (int i = 0; i < n; i++) {
int l = -1, r = n + 1;
while (l + 1 < r) {
int mid = (l + r) / 2, x = i;
for (int j = 20; j >= 0; j--) {
if (mid & (1 << j)) {
x = up[x][j];
}
}
if (v[x].second - v[i].first + 1 >= m) {
ans = min(ans, mid);
r = mid;
}
else l = mid;
}
}
if (ans == 1e9)cout << -1 << endl;
else cout << ans+1 << endl;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(nullptr);
cout.tie(nullptr);
ll t = 1;
//cin >> t;
while (t--) {
solve();
}
}
