#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define vi vector<ll>
#define vvi vector<vector<ll>>
#define vs vector<string>
#define vc vector<char>
#define vb vector<bool>
#define vp vector<pair<ll, ll>>
#define vpp vector<pair<ll, pair<ll, ll>>>
#define pp pair<ll, ll>
#define qi queue<ll>
#define qp queue<pp>
#define pqi priority_queue<ll>
#define pqp priority_queue<pp>
#define mi map<ll, ll>
#define mpi map<pp, ll>
#define mip map<ll, pp>
#define mp map<pp, pp>
#define mb map<ll, bool>
#define si set<ll>
#define sp set<pp>
#define sc set<char>
#define mod 1000000007
#define inf INT_MAX
#define all(x) (x).begin(), (x).end()
ll get_max(ll l, ll r, ll k, ll a, ll b, vi& tree) {
if(r < a || b < l) return -1;
if(a <= l && r <= b) return tree[k];
ll d = (l + r) / 2;
return max(get_max(l, d, 2 * k, a, b, tree), get_max(d + 1, r, 2 * k + 1, a, b, tree));
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
ll n, m;
cin >> n >> m;
vp a(n);
si times;
for(int i = 0; i < n; i++) {
cin >> a[i].first >> a[i].second;
if(a[i].first > a[i].second) a[i].second += m;
times.insert(a[i].first);
times.insert(a[i].second);
}
vi coor2;
mi coor;
for(auto time : times) {
coor[time] = coor2.size();
coor2.push_back(time);
}
ll size = pow(2, ceil(log2(int(times.size()))));
vi tree(size * 2, -1);
for(int i = 0; i < n; i++) {
ll start = coor[a[i].first];
ll end = coor[a[i].second];
tree[start + size] = end;
}
for(int i = size - 1; i > 0; i--) {
tree[i] = max(tree[i * 2], tree[i * 2 + 1]);
}
ll ans = inf;
for(auto[start, end] : a) {
ll l = coor[start], r = coor[end];
ll cur = 1;
while(true) {
ll mx = get_max(0, size - 1, 1, l, r, tree);
if(mx <= r) {
cur = inf;
break;
}
ll real = coor2[mx];
cur++;
if(real >= start + m) break;
l = r;
r = mx;
}
ans = min(ans, cur);
}
if(ans == inf) ans = -1;
cout << ans << '\n';
return 0;
}
/*
4 100
11 30
0 9
9 0
4 5
2
*/
