///*** Sown_Vipro ***///
/// ->TEAM SELECTION TEST<- ///
#include<bits/stdc++.h>
using namespace std;
//#pragma GCC optimize ("O3")
//#pragma GCC optimize ("unroll-loops")
//#pragma GCC target("popcnt")
#define F first
#define S second
#define pb push_back
#define pi pair<int, int>
#define pii pair<int, pair<int, int> >
#define FOR(i, a, b) for(int i = a; i <= b; ++i)
#define REP(i, a, b) for(int i = a; i >= b; --i)
#define all(s) s.begin(), s.end()
#define szz(s) int(s.size())
//#define int long long
const string NAME = "sown";
const int N = 2e6 + 5, MAX = 1e6, MOD = 1e9 + 7;
void maxi(int &x, int y){ if(x < y) x = y; }
void mini(int &x, int y){ if(x > y) x = y; };
void add(int &x, int y){ x += y; x += MOD * (x < 0); x -= MOD * (x >= MOD); };
int n, m, M;
pi e[N], s[N];
int st[4 * N], p[30][N];
int Merge(int A, int B){
if(s[A].S > s[B].S) return A;
return B;
}
void update(int id, int l, int r, int i, int x){
if(l > i || r < i) return;
if(l == r){
st[id] = Merge(st[id], x);
// cout << st[id] << " " << x << "\n";
return;
}
int m = (l + r) / 2;
update(2 * id, l, m, i, x);
update(2 * id + 1, m + 1, r, i, x);
st[id] = Merge(st[2 * id], st[2 * id + 1]);
}
int get(int id, int l, int r, int u, int v){
if(l > v || r < u) return 0;
if(u <= l && r <= v) return st[id];
int m = (l + r) / 2;
return Merge(get(2 * id, l, m, u, v), get(2 * id + 1, m + 1, r, u, v));
}
vector<int> tmp;
void solve(){
cin >> n >> M;
tmp.pb(0);
tmp.pb(M);
FOR(i, 1, n){
cin >> e[i].F >> e[i].S;
tmp.pb(e[i].F);
tmp.pb(e[i].S);
if(e[i].F <= e[i].S){
s[++m] = e[i];
}else{
s[++m] = {0, e[i].S};
s[++m] = {e[i].F, M};
// cout << e[i].F << " " << M <<C "\n";
}
}
sort(s + 1, s + 1 + m);
sort(all(tmp));
tmp.erase(unique(all(tmp)), tmp.end());
// cout << Merge(0, 1);
REP(i, m, 1){
int l = lower_bound(all(tmp), s[i].F) - tmp.begin() + 1;
int r = lower_bound(all(tmp), s[i].S) - tmp.begin() + 1;
// cout << s[i].F << " " << s[i].S << "\n";
p[0][i] = get(1, 1, szz(tmp), l, r);
// cout << i << " " << p[0][i] << "\n";
update(1, 1, szz(tmp), l, i);
}
FOR(k, 1, 20) FOR(i, 1, m) p[k][i] = p[k - 1][p[k - 1][i]];
e[n + 1] = {M, 0};
int ans = 1e9;
FOR(i, 1, n + 1){
if(e[i].F <= e[i].S) continue;
swap(e[i].F, e[i].S);
int l = lower_bound(all(tmp), 0) - tmp.begin() + 1;
int r = lower_bound(all(tmp), e[i].F) - tmp.begin() + 1;
// cout << e[i].F + 1 << " " << l << " " << r << '\n';
int u = get(1, 1, szz(tmp), l, r), res = (i != n + 1);
// cout << u << "\n";
REP(k, 20, 0){
int v = p[k][u];
// cout << k << " " << v << "\n";
if(v && s[v].S < e[i].S){
u = v;
res += (1 << k);
}
}
if(s[u].S >= e[i].S){
ans = min(ans, res + 1);
}
if(s[p[0][u]].S >= e[i].S){
ans = min(ans, res + 2);
}
// cout << res << " " << s[u].S << " " << s[p[0][u]].S << " " << e[i].S << "\n";
// break;
}
if(ans == 1e9) cout << -1;
else
cout << ans;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
if(fopen((NAME + ".inp").c_str(), "r")){
freopen((NAME + ".inp").c_str(), "r", stdin);
freopen((NAME + ".out").c_str(), "w", stdout);
}
int t = 1;
// cin >> t;
while(t--){
solve();
}
}
