#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
#define fi first
#define se second
#define vi vector<int>
#define vll vector<long long>
#define pii pair<int, int>
#define pll pair<long long, long long>
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define all(x) (x).begin(), (x).end()
#define sz(x) (int)(x).size()
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng64(chrono::steady_clock::now().time_since_epoch().count());
inline int rand(int l,int r){return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l,ll r){return uniform_int_distribution<ll>(l, r)(rng64);}
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
struct custom_hash {
static uint64_t splitmix64(uint64_t x) {
x += 0x9e3779b97f4a7c15;
x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
return x ^ (x >> 31);
}
size_t operator()(uint64_t x) const {
static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
return splitmix64(x + FIXED_RANDOM);
}
};
struct Info{
ll ind, blokSz, blokMod, val;
Info(ll nind, ll nb, ll nm, ll nv){
ind = nind;
blokSz = nb;
blokMod = nm;
val = nv;
}
};
const int MAXN = 5e5 + 7;
const int MAXK = 20;
const int BASE = (1 << 19);
pii tree[2 * BASE + 7];
int p[MAXN];
int e[MAXN];
int nxt[MAXN];
int jump[MAXK][MAXN];
pii mx[MAXN];
int n, m;
void init(){
for(int i = 1; i <= n; i++){
tree[i + BASE] = {e[i], i};
}
for(int i = BASE - 1; i >= 1; i--){
if(tree[2 * i].fi >= tree[2 * i + 1].fi){
tree[i] = tree[2 * i];
}else{
tree[i] = tree[2 * i + 1];
}
}
}
pii query(int v, int l, int r, int a, int b){
if(r < a || b < l){
return mp(0, 0);
}
if(a <= l && r <= b){
return tree[v];
}
int mid = (l + r) / 2;
pii r1 = query(2 * v, l, mid, a, b);
pii r2 = query(2 * v + 1, mid + 1, r, a, b);
if(r1.fi >= r2.fi){
return r1;
}
return r2;
}
int main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
cin >> n >> m;
vector<pii> vec;
for(int i = 1; i <= n; i++){
cin >> p[i] >> e[i];
if(p[i] < e[i]){
vec.pb({p[i], e[i]});
vec.pb({p[i] + m, e[i] + m});
}else{
vec.pb({p[i], e[i] + m});
vec.pb({p[i] + m, e[i] + 2 * m});
}
}
n *= 2;
sort(all(vec));
//cerr << sz(vec) << ' ' << n << '\n';
for(int i = 1; i <= n; i++){
p[i] = vec[i - 1].fi;
e[i] = vec[i - 1].se;
}
//cerr << "NIGGA\n";
init();
nxt[n] = n;
/*cout << "-------\n";
for(int i = 1; i <= n; i++){
cout << p[i] << ' ' << e[i] << '\n';
}*/
for(int i = n - 1; i >= 1; i--){
if(p[i + 1] > e[i]){
nxt[i] = i;
continue;
}
//cout << "----\n";
int l = i + 1;
int hi = n;
int s;
while(l < hi){
//cout << l << ' ' << hi << '\n';
s = (l + hi + 1) / 2;
if(p[s] <= e[i]){
l = s;
}else{
hi = s - 1;
}
}
//cout<< i << ' ' << l << '\n';
pii r = query(1, 0, BASE - 1, i + 1, l);
nxt[i] = r.se;
}
for(int i = 1; i <= n; i++){
jump[0][i] = nxt[i];
}
for(int j = 1; j < MAXK; j++){
for(int i = 1; i <= n; i++){
jump[j][i] = jump[j - 1][jump[j - 1][i]];
}
}
// cout << "----\n";
int ans = (int)1e9;
for(int i = 1; i <= n; i++){
if(e[jump[MAXK - 1][i]] - p[i] < m){
continue;
}
//cout << "--\n";
//cout << i << ' ' << nxt[i] << '\n';
int r = 1;
int v = i;
for(int j = MAXK - 1; j >= 0; j--){
if(e[jump[j][v]] - p[i] < m){
r += (1 << j);
v = jump[j][v];
}
}
r++;
//cout << v << ' ' << r<< '\n';
ans = min(ans, r);
}
if(ans == (int)1e9){
cout << -1 << '\n';
}else{
cout << ans << '\n';
}
return 0;
}
