///huynhocute123///
#include<bits/stdc++.h>
using namespace std;
#define S second
#define F first
#define pii pair<long long ,long long >
#define piii pair<int,pair<int,int>>
#define pb push_back
#define FOR(i, a, b) for(int i = a; i <= b; ++i)
#define REP(i, a, b) for(int i = b; i >= a; --i)
#define ALL(v) v.begin(),v.end()
#define inp(name) if(fopen(name, "r")) freopen(name, "r", stdin);
#define out(name) if(fopen(name, "w")) freopen(name, "w", stdout);
//random_device rd;
//mt19937 rng(rd());
//#pragma GCC optimize ("O3")
//#pragma GCC optimize ("unroll-loops")
//#pragma GCC target("popcnt")
//#define int long long
const int MAX = 1e9+9;
const long long MAXLL = 1e18+9;
const double pi = 3.14159265358979323846;
const double rad = 3.14159265358979323846 /180;
bool minimize(int &u, int v){
if(v < u){
u = v;
return 1;
}
return 0;
}
bool maximize(int &u, int v){
if(v > u){
u = v;
return 1;
}
return 0;
}
bool maximizell(long long &u, long long v){
if(v > u){
u = v;
return 1;
}
return 0;
}
bool minimizell(long long &u, long long v){
if(v < u){
u = v;
return 1;
}
return 0;
}
const int mod = 1e9 + 7;
inline int fastPow(int a, int n){
if(n == 0) return 1;
int t = fastPow(a, n >> 1);
t = 1ll * t * t % mod;
if(n & 1) t = 1ll * t * a % mod;
return t;
}
inline void Add(int& x ,int y){
x += y;
if(x >= mod)x -=mod;
}
inline void Sub(int& x, int y){
x-= y;
if(x < 0)x += mod;
}
const int maxN = 8 * 1e5 + 999 ;
long long n , m ;
pii shift[maxN];
vector<int> ar;
namespace sub1{
bool check(){
return (n <= 20);
}
struct sweep{
long long pos, kk;
bool operator <(const sweep& rhs)const{
if(pos != rhs.pos)return pos < rhs.pos;
return kk < rhs.kk;
}
};
vector<sweep>line;
bool lmao(){
sort(ALL(line));
// for(auto [x , y] : line )cout << x << " " << y << '\n';
// cout << '\n';
int cnt =0 ;
if(line[0].pos != 0)return 0;
for(auto x : line){
cnt += x.kk;
if(cnt == 0)return 0;
}
return (cnt >= 1);
}
void solve(){
int ans = MAX;
FOR(mask , 1 , (1 << n) - 1){
line.clear();
FOR(i, 1, n){
if( ((mask >> (i - 1)) & 1) == 1){
if(shift[i].F < shift[i].S){
line.pb({shift[i].F , 1});
if(shift[i].S + 1 <= m)line.pb({shift[i].S + 1 , -1});
}else{
line.pb({0 ,1});
line.pb({shift[i].S + 1 , -1});
line.pb({shift[i].F , 1});
}
}
}
// cout << mask << '\n';
if(lmao())minimize(ans, __builtin_popcount(mask));
}
cout << (ans == MAX ? -1 : ans);
}
}
namespace sub2{
long long start = MAXLL, End;
struct sweep{
long long pos, kk;
bool operator <(const sweep& rhs)const{
return pos < rhs.pos;
}
};
vector<sweep>line;
int mn[4 * maxN];
int lazy[4 * maxN];
void init(int id ,int l ,int r){
mn[id] = MAX;
lazy[id] =MAX;
if(l == r)return;
int mid = (l + r)/2;
init(id << 1 , l ,mid);
init(id<< 1 | 1, mid + 1, r);
}
void push(int id){
if(lazy[id] >= MAX)return;
minimize(lazy[id << 1] , lazy[id]);
minimize(lazy[id << 1 | 1] , lazy[id]);
minimize(mn[id << 1] , lazy[id]);
minimize(mn[id << 1 | 1] , lazy[id]);
lazy[id] = MAX;
}
void upd(int id ,int l ,int r, int u ,int v ,int val){
if(v < l || u > r)return;
if(u <= l && r <= v){
minimize(mn[id] ,val);
minimize(lazy[id] , val);
return;
}
int mid = (l +r)/2;
push(id);
upd(id << 1 ,l ,mid ,u ,v, val);
upd(id << 1 | 1,mid + 1, r, u ,v , val);
minimize(mn[id], mn[id << 1 ]);
minimize(mn[id], mn[id << 1 | 1]);
}
int get(int id ,int l ,int r , int u ,int v){
if(v < l || u > r)return MAX;
if(u <= l &&r <= v)return mn[id];
int mid = (l + r)/2;
push(id);
return min(get(id << 1 , l,mid ,u ,v ) , get(id << 1 | 1,mid + 1, r, u ,v));
}
void solve(){
FOR(i, 1, n){
if(shift[i].F > shift[i].S){
shift[i].S += m;
}else{
shift[i].S += m;
shift[i].F += m;
}
assert(shift[i].F < shift[i].S);
minimizell(start , shift[i].F);
// cout << shift[i].F << " " << shift[i].S << '\n';
}
End = start + m;
// cerr << start << " "<< End << '\n';
FOR(i, 1, n){
line.pb({shift[i].F , i});
ar.pb(shift[i].F);
ar.pb(shift[i].S);
}
ar.pb(start);
ar.pb(End);
sort(ALL(line));
sort(ALL(ar));
ar.erase(unique(ALL(ar)),ar.end());
int sz = ar.size() + 2;
init(1 , 1 , sz);
int id = lower_bound(ALL(ar) , start) - ar.begin() + 1;
upd(1, 1, sz, id, id, 0);
for(auto [tick , id] : line){
int r = shift[id].S;
r = lower_bound(ALL(ar), shift[id].S) - ar.begin() + 1;
int l = lower_bound(ALL(ar), shift[id].F) - ar.begin() + 1;
int val = get(1, 1 , sz, l , sz);
upd(1, 1, sz , l , r ,val + 1);
}
int pos = lower_bound(ALL(ar) , End) - ar.begin() + 1;
int ans = get(1, 1, sz , pos, sz);
cout << (ans > n ? -1 : ans);
cerr << (ans > n ? -1 : ans);
// cout << start << '\n';
}
}
inline void solve(){
cin >> n >> m ;
FOR(i, 1, n){
long long u ,v;cin >> u >> v;
shift[i] = {u ,v};
}
// if(sub1::check())return sub1::solve();
// if(sub2::check())return sub2::solve();
return sub2::solve();
}
#define NAME "task"
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
if(fopen(NAME".inp", "r")){
freopen(NAME".inp", "r" ,stdin);
freopen(NAME".out", "w" ,stdout);
}
int tc = 1;
// cin >> tc;
while( tc-- )solve();
cerr << '\n' << "Time elapsed: " << (1.0 * clock() / CLOCKS_PER_SEC) << " s\n" ;
}
