#include <bits/stdc++.h>
using namespace std;
const int maxN = 2e5 + 5;
pair<int, int> p[maxN];
int s[maxN], jump[20][maxN];
struct node {
int val, id;
} st[maxN << 4];
node Merge(node A, node B) {
if (A.val >= B.val) return A;
return B;
}
void build(int id, int l, int r) {
if (l == r) {
st[id].val = p[l].second;
st[id].id = l;
return ;
}
int mid = (l + r) >> 1;
build(id << 1, l, mid);
build(id << 1 | 1, mid + 1, r);
st[id] = Merge(st[id << 1], st[id << 1 | 1]);
}
node get(int id, int l, int r, int u, int v) {
if (v < l || r < u) return {-100, 0};
if (u <= l && r <= v) return st[id];
int mid = (l + r) >> 1;
node A = get(id << 1, l, mid, u, v);
node B = get(id << 1 | 1, mid + 1, r, u, v);
return Merge(A, B);
}
int main() {
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int n, m;
cin >> n >> m;
for (int i = 1; i <= n; i++) {
cin >> p[i].first >> p[i].second;
if (p[i].first > p[i].second) p[i].second += m;
}
sort(p + 1, p + n + 1);
build(1, 1, n);
for (int i = 1; i <= n; i++)
s[i] = p[i].first;
for (int i = 1; i <= n; i++) {
int l = lower_bound(s + 1, s + n + 1, p[i].first) - s;
int r = upper_bound(s + 1, s + n + 1, p[i].second) - s - 1;
node res = get(1, 1, n, l, r);
if (res.val <= p[i].second) continue;
jump[0][i] = res.id;
}
for (int k = 1; k <= 17; k++)
for (int i = 1; i <= n; i++)
jump[k][i] = jump[k - 1][jump[k - 1][i]];
int ans = 1e9;
for (int i = 1; i <= n; i++) {
int id = i, goal = p[i].first + m, res = 0;
for (int k = 17; k >= 0; k--) {
int nxt = jump[k][id];
if (nxt == 0 || p[nxt].second >= goal) continue;
res += (1 << k);
id = nxt;
}
res++; id = jump[0][id];
if (p[id].second >= goal) ans = min(ans, res);
}
if (ans == 1e9) cout << -1 << '\n';
else cout << ans + 1 << '\n';
return 0;
}
