#include <bits/stdc++.h>
using namespace std;
const int inf = int(1e9);
const int N = 5009 * 50;
int id = 1;
int sum[N];
int lazy[N];
int L[N];
int R[N];
void push(int nd, int l, int r) {
if (!L[nd]) {
L[nd] = ++id;
R[nd] = ++id;
}
if (lazy[nd] == 0) return;
int mid = (l + r) / 2;
sum[L[nd]] = (mid - l + 1) * lazy[nd];
sum[R[nd]] = (r - mid) * lazy[nd];
lazy[L[nd]] = lazy[nd];
lazy[R[nd]] = lazy[nd];
}
void upd(int nd, int l, int r, int x, int y) {
push(nd, l, r);
if (x <= l && r <= y) {
sum[nd] = r - l + 1;
lazy[nd] = 1;
return;
}
if (l > y || r < x) {
return;
}
int mid = (l + r) / 2;
upd(L[nd], l, mid, x, y);
upd(R[nd], mid + 1, r, x, y);
sum[nd] = sum[L[nd]] + sum[R[nd]];
}
int get(int nd, int l, int r, int x, int y) {
push(nd, l, r);
if (x <= l && r <= y) {
return sum[nd];
}
if (l > y || r < x) {
return 0;
}
int mid = (l + r) / 2;
return get(L[nd], l, mid, x, y) + get(R[nd], mid + 1, r, x, y);
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<int> s(n), e(n);
for (int i = 0; i < n; i++) {
cin >> s[i] >> e[i];
}
int ans = -1;
for (int z = 1; z <= n; z++) {
int mx = 0;
int idx = -1;
for (int i = 0; i < n; i++) {
if (s[i] <= e[i]) {
int x = get(1, 0, inf, s[i], e[i]);
if (e[i] - s[i] + 1 - x > mx) {
mx = e[i] - s[i] + 1 - x;
idx = i;
}
//cout << "z: " << z << ' ' << "i: " << i << ' ' << "points: " << e[i] - s[i] + 1 - x << ' ' << "mx: " << mx << ' ' << "idx: " << idx << '\n';
} else {
int x = get(1, 0, inf, 0, e[i]) + get(1, 0, inf, s[i], m - 1);
//cout << "z: " << z << ' ' << "i: " << i << ' ' << "x: " << x << ' ' << "res: " << s[i] + 1 + m - e[i] + 1 << '\n';
if (e[i] + 1 + m - s[i] - x > mx) {
mx = e[i] + 1 + m - s[i] - x;
idx = i;
}
//cout << "z: " << z << ' ' << "i: " << i << ' ' << "points: " << s[i] + 1 + m - e[i] + 1 - x << ' ' << "mx: " << mx << ' ' << "idx: " << idx << '\n';
}
}
if (idx == -1) break;
if (s[idx] > e[idx]) {
upd(1, 0, inf, 0, e[idx]);
upd(1, 0, inf, s[idx], m - 1);
} else {
upd(1, 0, inf, s[idx], e[idx]);
}
if (sum[1] == m) {
ans = z;
break;
}
//cout << "idx: " << idx << ' ' << "sum[1]: " << sum[1] << '\n';
}
cout << ans << '\n';
return 0;
}
