#include <bits/stdc++.h>
#define pb push_back
#define f first
#define sc second
using namespace std;
typedef long long int ll;
typedef string str;
int main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, m; cin >> n >> m;
vector<pair<int, int>> A(n);
for(auto &[x, y]: A){
cin >> x >> y;
if(x > y) y+=m;
}
sort(A.begin(), A.end());
map<int, vector<int>> L, R;
for(int i = 0; i < n; i++){
L[A[i].first].push_back(i);
if(A[i].second < m) R[A[i].second].push_back(i);
}
vector<int> nxt(n, -1);
set<pair<int, int>> st;
while(!L.empty() || !R.empty()){
if(R.empty() || (!L.empty() && L.begin()->first <= R.begin()->first)){
auto [t, a] = *L.begin();
L.erase(L.begin());
for(int i: a) st.insert({A[i].second, i});
}
else{
auto [t, a] = *R.begin();
R.erase(R.begin());
for(int i: a){
st.erase({A[i].second, i});
int mx = A[i].second, j = -1;
for(auto [_, k]: st){
if(A[k].first > A[i].first && A[k].second > mx) mx = A[k].second, j = k;
}
nxt[i] = j;
}
}
}
vector<int> cnt(n, 0), mx(n, 0);
int ans = 1e9;
for(int i = n-1; i >= 0; i--){
if(nxt[i] == -1){
if(A[i].second >= m) cnt[i] = 1, mx[i] = A[i].second-m;
}
else if(cnt[nxt[i]] != 0){
cnt[i] = cnt[nxt[i]]+1;
mx[i] = mx[nxt[i]];
if(mx[i] >= A[i].first) ans = min(ans, cnt[i]);
}
}
if(ans > n) ans = -1;
cout << ans << "\n";
}
