#include <bits/stdc++.h>
#define all(x) x.begin(), x.end()
#define len(s) (ll) s.size()
#define pb push_back
#define F first
#define S second
using namespace std;
typedef long long ll;
const int N = 2e5 + 17;
const int P = 31;
const int mod = 1e9 + 7;
const ll inf = 1e18;
ll n, m;
ll l[N], r[N], ord[N];
bool cmp(ll i, ll j){
return l[i] < l[j];
}
signed main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
for(ll i = 1; i <= n; i++){
cin >> l[i] >> r[i], ord[i] = i;
if(r[i] < l[i]) r[i] = m;
}
sort(ord + 1, ord + n + 1, cmp);
ll fin = 0, next_fin = -1, res = 0;
for(ll _i = 1; _i <= n; _i++){
ll i = ord[_i];
if(l[i] <= fin){
next_fin = max(next_fin, r[i]);
}
else{
if(next_fin <= fin) { cout << -1; return 0; }
fin = next_fin, res++, _i--;
if(fin == m) break;
}
if(next_fin == m){
res++;
break;
}
}
cout << res;
}
