#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
typedef long long int ll;
typedef vector<ll> vi;
typedef vector<vector<ll>> vvi;
typedef pair<ll,ll> pi;
typedef map<ll,ll> mi;
typedef long double ld;
typedef vector<ld> vd;
typedef vector<vector<ld>> vvd;
typedef pair<ld,ld> pd;
#define ff first
#define ss second
#define srt(a) sort(a.begin(),a.end());
#define fip(k, n) for (ll i = k; i < n; i++)
#define fjp(k, n) for (ll j = k; j < n; j++)
#define fin(k, n) for (ll i = k; i >= n; i--)
#define fjn(k, n) for (ll j = k; j >= n; j--)
#define fp(k, n, m) for (ll k = n; k < m; k++)
#define fn(k, n, m) for (ll k = n; k >= m; k--)
#define ordered_set tree<pi, null_type,less< pi >, rb_tree_tag,tree_order_statistics_node_update>
#define totalOne(n) __builtin_popcount(n)
#define backZero(n) __builtin_ctzll(n)
#define frontZero(n) __builtin_clzll(n)
#define fx(k) for ( auto x : k )
#define test ll t;cin >> t;while (t--)
#define nli "\n"
// ==========================(debug)============================================================================================== //
#ifndef ONLINE_JUDGE
#define debug(x) cerr << #x <<" "; _printn(x); cerr << nli;
#else
#define debug(x)
#endif
void _printn(ll x){ cerr<<x<<" "; }
void _printn(int x){ cerr<<x<<" "; }
void _printn(ld x){ cerr<<x<<" "; }
void _printn(double x){ cerr<<x<<" "; }
void _printn(string x){ cerr<<x<<" "; }
void _printn(char x){ cerr<<x<<" "; }
void _printn(bool x){ cerr<<x<<" "; }
template<class T,class V>void _printn(pair<T,V> vv);
template<class T> void _printn(vector<T> vv);
template<class T> void _printn(set<T> vv);
template<class T,class V> void _printn(map<T,V> vv);
template<class T> void _printn(multiset<T> vv);
template<class T,class V>void _printn(pair<T,V> vv){ cerr<<"( ";_printn(vv.ff);cerr<<",";_printn(vv.ss);cerr<<")";}
template<class T> void _printn(vector<T> vv){ cerr<<"[ "; for(auto xx:vv){ _printn(xx);cerr<<" "; } cerr<<"]"; };
template<class T> void _printn(set<T> vv){ cerr<<"{ "; for(auto xx:vv){ _printn(xx);cerr<<" "; } cerr<<"}"; };
template<class T> void _printn(multiset<T> vv){ cerr<<"{ "; for(auto xx:vv){ _printn(xx);cerr<<" "; } cerr<<"}"; };
template<class T,class V> void _printn(map<T,V> vv){ cerr<<"{ "; for(auto xx:vv){ _printn(xx);cerr<<" "; } cerr<<"}"; };
// ==========================(debug)============================================================================================== //
ll n,m,tp,tp2,res,cnt,sum,tptp,ans;
const ll mx = 5e5+5;
const ll mod = 1e9+7;
// ==========================(MOD)=============================================================================================== //
ll mod_add(ll aa,ll bb){ return ((aa%mod)+(bb%mod))%mod; }
ll mod_minus(ll aa,ll bb){ return (((aa%mod)-(bb%mod))+10*mod)%mod; }
ll mod_mul(ll aa,ll bb){ return ((aa%mod)*(bb%mod))%mod; }
ll mod_power(ll aa,ll bb){ aa%=mod; ll empowered = 1; bb%=mod-1; while(bb > 0){ if(bb & 1) empowered = mod_mul(empowered,aa); bb = bb >> 1; aa = mod_mul(aa,aa); } return empowered; }
ll mod_divi(ll aa,ll bb){ aa=mod_mul(aa,mod_power(bb,mod-2)); return aa; }
// ==========================(MOD)=============================================================================================== //
bool f = false;
vector<pi> lis,ls;
ll to[mx][20];
typedef struct SEGMENT_TREE{
vector<pi> arr;
ll range;
void init(ll k){
range = 4*k;
arr.resize(range);
fip(0,range)
arr[i] = {-1e18,-1e18};
return;
}
void update(ll ptr,ll l,ll r,ll pos,ll va,ll vb){
// debug(ptr);
// debug(range);
if(l==r && l==pos){
arr[ptr] = {va,vb};
return;
}
if(l>pos || r<pos)
return;
ll mid = l + (r-l) / 2;
update(2*ptr,l,mid,pos,va,vb);
update(2*ptr+1,mid+1,r,pos,va,vb);
arr[ptr] = max(arr[2*ptr],arr[2*ptr+1]);
return;
}
pi query(ll ptr,ll l,ll r,ll st,ll en){
if(l>en || r<st)
return {-1e18,-1e18};
if(l>=st && r<=en)
return arr[ptr];
ll mid = l + (r-l) / 2;
return max(query(2*ptr,l,mid,st,en),query(2*ptr+1,mid+1,r,st,en));
}
void deb(ll ptr,ll l,ll r){
cerr<<ptr<<" "<<l<<" "<<r<<nli;
debug(arr[ptr]);
if(l==r)
return;
ll mid = l + (r-l) / 2;
deb(2*ptr,l,mid);
deb(2*ptr+1,mid+1,r);
return;
}
}SGT;
SGT sgt;
vi v;
ll l,r,mid,pt,pt2;
pi get(ll x,ll y){
l = 0;
r = v.size() - 1;
pt = r+1;
while(l<=r){
mid = l + (r-l) / 2;
if(v[mid]>=x){
pt = mid;
r = mid - 1;
}
else
l = mid + 1;
}
l = 0;
r = v.size() - 1;
pt2 = r+1;
while(l<=r){
mid = l + (r-l) / 2;
if(v[mid]<=y){
pt2 = mid;
l = mid + 1;
}
else
r = mid - 1;
}
return {pt,pt2};
}
int main(){
ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
// #ifndef ONLINE_JUDGE
// freopen("input1.txt", "r", stdin);
// freopen("output1.txt", "w", stdout);
// freopen("error1.txt", "w", stderr);
// #endif // ONLINE_JUDGE
cin>>n>>m;
fip(0,n){
cin>>tp>>tp2;
if(tp2<tp)
tp2+=m;
lis.push_back({tp,tp2});
v.push_back(tp);
}
srt(lis);
srt(v);
sgt.init(n);
ans = 1e18;
fip(0,(ll)lis.size()){
tp = lis[i].ff;
tp = get(tp,tp).ff;
// debug(tp);
sgt.update(1,0,n-1,tp,lis[i].ss,i);
}
// sgt.deb(1,0,n-1);
// // priority_queue<pi> pq;
pi p;
fip(0,(ll)lis.size()){
tp = -1e18;
tp2 = -1;
p = get(lis[i].ff,lis[i].ss);
// debug(p);
p = sgt.query(1,0,n-1,p.ff,p.ss);
// debug(p);
tp2 = p.ss;
to[i][0] = tp2;
}
// fip(0,n)
// cout<<to[i][0]<<" ";
// cout<<nli;
fjp(1,20)
fip(0,n)
to[i][j] = to[to[i][j-1]][j-1];
fip(0,(ll)lis.size()){
tp = i;
tp2 = lis[i].ff+m;
cnt = 0;
fjn(19,0){
if(lis[to[tp][j]].ss<tp2){
tp = to[tp][j];
cnt |= (1<<j);
}
}
tp = to[tp][0];
cnt++;
cnt++;
// debug(tp2);
// debug(cnt);
// cerr<<nli;
if(lis[tp].ss>=tp2)
ans = min(ans,cnt);
}
if(ans==1e18)
ans = -1;
cout<<ans<<nli;
cerr << "Time elapsed: " << setprecision(6) << 1000.0 * clock() / CLOCKS_PER_SEC << "ms\n";
return 0;
}
