#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define MASK(i) (1ULL << (i))
#define GETBIT(mask, i) (((mask) >> (i)) & 1)
#define ALL(v) (v).begin(), (v).end()
#define block_of_code if(true)
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll gcd(ll a, ll b){return __gcd(a, b);}
ll LASTBIT(ll mask){return (mask) & (-mask);}
int pop_cnt(ll mask){return __builtin_popcountll(mask);}
int ctz(ull mask){return __builtin_ctzll(mask);}
int logOf(ull mask){return 63 - __builtin_clzll(mask);}
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rngesus(ll l, ll r){return l + (ull) rng() % (r - l + 1);}
template <class T1, class T2>
bool maximize(T1 &a, T2 b){
if (a < b) {a = b; return true;}
return false;
}
template <class T1, class T2>
bool minimize(T1 &a, T2 b){
if (a > b) {a = b; return true;}
return false;
}
template <class T>
void printArr(T container, string separator = " ", string finish = "\n", ostream &out = cout){
for(auto item: container) out << item << separator;
out << finish;
}
template <class T>
void remove_dup(vector<T> &a){
sort(ALL(a));
a.resize(unique(ALL(a)) - a.begin());
}
const int N = 2e5 + 69;
const int LOG_N= 18;
const int INF = MASK(LOG_N);
int n, m;
int nxt[LOG_N][N];
int pref[N];
int main(void){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
vector<pair<int,int>> a(n);
for(int i = 0; i<n; ++i) {
int l, r; cin >> l >> r;
if (l > r) r += m;
a[i] = {l, r};
}
sort(ALL(a));
pref[0] = 0;
for(int i = 1; i<n; ++i){
pref[i] = pref[i-1];
if (a[pref[i]].second < a[i].second) pref[i] = i;
}
for(int i = 0; i<n; ++i){
int idx = lower_bound(ALL(a), make_pair(a[i].second + 1, -1)) - a.begin() - 1;
idx = pref[idx];
nxt[0][i] = idx;
}
for(int j = 1; j < LOG_N; ++j) for(int i = 0; i<n; ++i)
nxt[j][i] = nxt[j-1][nxt[j-1][i]];
int ans = INF;
for(int i = 0; i<n; ++i){
int cu = 0;
int u = i;
for(int j = LOG_N - 1; j>=0; --j) {
int v = nxt[j][u];
if (a[v].second < a[i].first + m) {
cu += MASK(j);
u = v;
}
}
minimize(ans, cu + 2);
}
if (ans > n) ans = -1;
cout << ans << "\n";
return 0;
}
