#include <bits/stdc++.h>
using namespace std;
int const MAX=2e5+5;
int n,m;
struct interval{
int l,r;
}v[MAX];
void read(){
cin>>n>>m;
int i;
for(i=1;i<=n;++i){
cin>>v[i].l>>v[i].r;
if(v[i].l>v[i].r)
v[i].r+=m;
}
}
struct event{
int ind;
bool tip; /// 1 0
bool operator<(event ot){
int nr1=((tip)?v[ind].l:v[ind].r);
int nr2=((ot.tip)?v[ot.ind].l:v[ot.ind].r);
if(nr1!=nr2)
return nr1<nr2;
return tip>ot.tip;
}
}ev[2*MAX];
int const LOG=20;
int rmq[MAX][LOG];
void put_fathers(){
int i;
for(i=1;i<=n;++i){
ev[2*i-1]={i,1};
ev[2*i]={i,0};
}
sort(ev+1,ev+2*n+1);
int best=0;
for(i=1;i<=2*n;++i){
int ind=ev[i].ind;
if(ev[i].tip){
if(v[best].r<v[ind].r)
best=ind;
}
else
rmq[ind][0]=best;
}
}
void build_rmq(){
int i,j;
for(j=1;j<LOG;++j)
for(i=1;i<=n;++i)
rmq[i][j]=rmq[rmq[i][j-1]][j-1];
}
int const INF=1e9;
int bin_lift(int nod){
int capat=v[nod].l+m;
int anc=0;
int bit;
for(bit=LOG-1;bit>=0;--bit)
if(v[rmq[nod][bit]].r<capat){
anc+=(1<<bit);
nod=rmq[nod][bit];
}
nod=rmq[nod][0];
if(v[nod].r>=capat)
return anc+2;
return INF;
}
void minself(int& x,int val){
if(x>val)
x=val;
}
int solve(){
int i;
int rasp=INF;
for(i=1;i<=n;++i)
minself(rasp,bin_lift(i));
if(rasp<INF)
return rasp;
return -1;
}
void write(int ans){
cout<<ans;
}
int main()
{
read();
put_fathers();
build_rmq();
write(solve());
return 0;
}
