/****ThanhCodeDao*****/
/*******Azazel*******/
#include<bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define pb push_back
#define checkbit(mask,i) ((mask>>i)&1)
#define bit(i) (1<<i)
#define MLog 21
#define all(v) v.begin(), v.end()
#define uni(v) v.erase(unique(all(v)), v.end())
typedef long long ll;
const ll maxN = 2e5+3, modd = 1e9+7;
struct Point {
ll x,y;
};
ll cross(Point p,Point q,Point r) { // vi tri r voi duong pq >0 la ben trai, =0 la thang hang
ll val = (q.x-p.x)*(r.y-q.y) - (q.y-p.y)*(r.x-q.x);
if(val < 0) return -1;
if(val > 0) return 1;
return 0;
}
ll dot(Point vecA,Point vecB) { // tra ve >0 la nhon, <0 la tu, =0 la vuong, 2 vecto phai chung goc
ll val = vecA.x*vecB.x + vecA.y*vecB.y;
if(val < 0) return -1;
if(val > 0) return 1;
return 0;
}
double triarea(Point p,Point q,Point r) { // cross(pq * pr) / 2
double cross = (q.x-p.x)*(r.y-q.y) - (q.y-p.y)*(r.x-q.x);
return fabs(cross)/2.0;
}
/* de cho
*/
/* nhan xet nho
*/
/* nhan xet tu thuat trau
*/
int n,m;
pair<int,int> p[maxN];
bool cmp(pair<int,int> p1, pair<int,int> p2) {
if(p1.F == p2.F) {
return p1.S < p2.S;
}
return p1.F < p2.F;
}
int ans = 1e9;
void dfs(int i,int finish,int &cnt,bool &isfinish) {
int j = i;
int mxr = 0, curchose = 0;
while(j+1<=n and p[i].F <= p[j+1].F and p[j+1].F <= p[i].S+1) {
if(p[j+1].S > mxr) {
mxr = p[j+1].S;
curchose = j+1;
}
++j;
}
++cnt;
if(cnt >= ans) return ;
if(i>n) return;
if(mxr >= finish) {
isfinish = true;
return;
} else {
if(curchose == 0) {
isfinish = false;
return;
}
dfs(curchose,finish,cnt,isfinish);
}
}
void sub3() {
for(int i = 1; i<=n; i++) {
bool isend = false;
int cnt = 1;
dfs(i,p[i].F + m,cnt,isend);
if(isend) {
ans = min(ans,cnt);
}
}
if(ans == 1e9) ans = -1;
cout << ans;
}
void solve() {
cin >> n >> m;
for(int i = 1; i<=n; i++) {
cin >> p[i].F >> p[i].S;
if(p[i].F > p[i].S) p[i].S += m;
}
sort(p+1,p+1+n,cmp);
// if(n<=5000) {
sub3();
return;
// }
// cout << -1;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
// freopen("inp.txt","r",stdin);
//freopen("out.txt","w",stdout);
solve();
return 0;
}
