#include <bits/stdc++.h>
#define ll long long
#define rep(i,m,n) for(int i=(m); i<=(n); i++)
#define reb(i,m,n) for(int i=(m); i>=(n); i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define MP make_pair
#define fs first
#define se second
#define bit(msk, i) ((msk >> i) & 1)
#define iter(id, v) for(auto id : v)
#define pb push_back
#define SZ(v) (int)v.size()
#define ALL(v) v.begin(),v.end()
using namespace std;
mt19937_64 rd(chrono :: steady_clock :: now ().time_since_epoch().count());
ll Rand (ll l, ll r) { return uniform_int_distribution<ll> (l, r) (rd); }
const int N = 2e5 + 7;
const int Mod = 1e9 + 7;
const int INF = 2e9 + 7;
const ll BASE = 137;
const int szBL = 320;
int m, n;
pii a[N];
int spt[N][25];
pii mx[N][25];
void solution () {
cin >> n >> m;
rep (i, 1, n) {
cin >> a[i].fs >> a[i].se;
if (a[i].se < a[i].fs) a[i].se = m + a[i].se;
}
sort (a + 1, a + 1 + n, [] (pii A, pii B) { return A.fs < B.fs || (A.fs == B.fs && A.se > B.se); });
rep (i, 1, n) {
mx[i][0] = MP(a[i].se, i);
}
for (int j = 1; (1 << j) <= n; ++j)
for (int i = 1; i + (1 << j) - 1 <= n; ++i)
mx[i][j] = max(mx[i][j - 1], mx[i + (1 << j - 1)][j - 1]);
auto get = [] (int L, int R) -> pii {
assert (L <= R);
int K = 31 - __builtin_clz(R - L + 1);
return max(mx[L][K], mx[R - (1 << K) + 1][K]);
};
rep (i, 1, n) {
int lf = i, rt = n;
while (lf < rt) {
int mid = lf + rt + 1 >> 1;
if (a[mid].fs <= a[i].se) lf = mid;
else rt = mid - 1;
}
spt[i][0] = get(i, lf).se;
// cout << i << " "<<spt[i][0] <<"\n";
}
rep (j, 1, 20)
rep (i, 1, n)
spt[i][j] = spt[spt[i][j - 1]][j - 1];
int ans = INF;
rep (i, 1, n) {
int toreach = m + a[i].fs;
int cur = i, res = 0;
reb (j, 20, 0) {
if (a[spt[cur][j]].se < toreach) {
cur = spt[cur][j];
res += (1 << j);
}
}
++res;
cur = spt[cur][0];
// cout << i<<" "<<cur <<" "<<toreach<<"\n";
if (a[cur].se >= toreach) ans = min(ans, res + 1);
}
if (ans == INF) cout << -1 <<"\n";
else cout << ans <<"\n";
}
#define file(name) freopen(name".inp","r",stdin); \
freopen(name".out","w",stdout);
int main () {
// file("c");
ios_base :: sync_with_stdio(false); cin.tie(0); cout.tie(0);
int num_Test = 1;
// cin >> num_Test;
while (num_Test--)
solution();
}
/*
no bug challenge +2
2 + 8 * 2 - 9
6 2
1 5 2 3 1 1
1 2 3 3 2
4 5
6 6
*/
