#include <bits/stdc++.h>
#define f first
#define s second
#define pb push_back
//#define mp make_pair
#define ll long long
using namespace std;
ll mod=1e9+7;
const ll N=2*1e5;
ll a[N+5],l,r,x,y,z,ans,t,n,q,mn,k,m,b[N+5],anss;
map <ll,ll> mx,mp,fix,c;
bool ok,okk;
set <ll> s;
pair <ll,ll> p[N+5],d[N+5];
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0),cout.tie(0);
cin>>n>>m;
for (int i=1; i<=n; i++){
cin>>p[i].f>>p[i].s;
}
sort(p+1,p+n+1);
for (int i=1; i<=n; i++){
if (p[i].f>p[i].s) b[0]=max(b[0],p[i].s),p[i].s+=m;
}
for (int i=1; i<=n; i++){
b[i]=max(b[i-1],p[i].s);
}
for (int i=1; i<=n; i++) a[i]=p[i].f;
for (int i=1; i<=n; i++){
x=p[i].s;
if (x>a[n]) y=n;
else y=upper_bound(a+1,a+n+1,x)-a-1;
mx[p[i].s]=b[y];
}
for (int i=0; i<=n; i++) b[i]=0;
ans=-1;
for (int i=1; i<=n; i++) c[p[i].s]=-1;
for (int i=1; i<=n; i++){
if (c[p[i].s]==-1) c[p[i].s]=p[i].f;
c[p[i].s]=min(c[p[i].s],p[i].f);
}
for (int i=1; i<=n; i++){
if (fix[p[i].s]==1) continue;
//pirvelia i
z=1;
x=p[i].s; ok=0; b[1]=x;
k=1;
d[k].f=p[i].f; d[k].s=1; ll cr=1;
okk=0;
anss=n+1;
while (fix[x]==0){
fix[x]=1;
y=mx[x];
if (y<=x){
ok=1; break;
}
x=y; z++;
y=c[x];
k++; d[k].f=y; d[k].s=z;
while (cr<=k && d[cr].f+m<=x+okk*m){
anss=min(anss,z-d[cr].s+1);
cr++;
}
if (x>m) okk=1,x-=m;
}
z=anss;
if (z>n) continue;
if (ans==-1) ans=z;
ans=min(ans,z);
}
cout<<ans<<endl;
}
