#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, m;
cin >> n >> m;
vector<pair<ll, ll>> seg;
seg.reserve(n << 1);
for (int i = 0; i < n; ++i) {
ll s, e;
cin >> s >> e;
if (s > e)
seg.emplace_back(s, e + m);
else
seg.emplace_back(s, e);
}
n = seg.size();
for (int i = 0; i < n; ++i) {
seg.emplace_back(seg[i].first + m, seg[i].second + m);
}
ranges::sort(seg);
n = seg.size();
vector<ll> l(n), r(n);
vector<int> pref(n + 1), nxt(n);
vector up(20, vector<int>(n));
for (int i = 0; i < n; ++i)
tie(l[i], r[i]) = seg[i];
for (int i = 1; i < n; ++i)
if (r[i] > r[pref[i - 1]])
pref[i] = i;
else
pref[i] = pref[i - 1];
for (int i = 0; i < n; ++i)
nxt[i] = pref[upper_bound(l.begin(), l.end(), r[i]) - l.begin() - 1];
up[0] = nxt;
for (int lg = 1; lg < 20; ++lg)
for (int i = 0; i < n; ++i)
up[lg][i] = up[lg - 1][up[lg - 1][i]];
ll ans = 1e12;
for (int i = 0; i < n; ++i) {
if (l[i] >= m)
continue;
ll target = l[i] + m, cnt = 1, cur = i;
if (r[i] >= target) {
ans = min(ans, cnt);
continue;
}
for (int lg = 20; lg--;) {
int to = up[lg][cur];
if (r[to] < target) {
cnt += (1 << lg);
cur = to;
}
}
cur = up[0][cur];
cnt++;
if (r[cur] >= target) {
ans = min(ans, cnt);
}
}
cout << (ans == 1e12 ? -1 : ans);
return 0;
}
