#include<bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define pb push_back
#define sz(x) (int)(x.size())
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
#define vi vector<int>
#define vp vector<pii>
#define vvi vector<vi>
#define ykh mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count())
#define __lg(x) 63-__builtin_clzll(x)
#define pow2(x) (1LL<<x)
void __print(int x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
void setIO(string s) {
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
#ifdef local
void CHECK();
void setio(){
freopen("/Users/iantsai/cpp/input.txt","r",stdin);
freopen("/Users/iantsai/cpp/output.txt","w",stdout);
}
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
void setio(){}
#define debug(x...)
#endif
#define TOI_is_so_de ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);setio();
const int mxn = 4e5+5;
const int inf = 1e18;
int n, m, l[mxn], r[mxn], nxt[mxn], st[20][mxn];
signed main(){
TOI_is_so_de;
cin >> n >> m;
for(int i=1;i<=n;i++){
cin >> l[i] >> r[i];
if(l[i] > r[i]) r[i] += m;
l[i+n] = l[i] + m;
r[i+n] = r[i] + m;
}
n *= 2;
{
vector<pii>temp;
for(int i=1;i<=n;i++){
temp.pb({l[i], -r[i]});
}
sort(all(temp));
int cnt = 0, end = -1;
for(auto [L, R] : temp){
R = -R;
if(R <= end){
continue;
}
l[++cnt] = L;
r[cnt] = R;
end = R;
}
n = cnt;
}
{
int id = 1;
vector<pii>temp;
for(int i=1;i<=n;i++){
temp.pb({l[i], i});
}
sort(all(temp));
for(int i=0;i<n;i++){
while(id<n and temp[id].F <= r[temp[i].S]){
id++;
}
st[0][temp[i].S] = temp[id-1].S;
}
}
{
for(int i=1;i<20;i++){
for(int j=1;j<=n;j++){
st[i][j] = st[i-1][st[i-1][j]];
}
}
}
int ans = inf;
for(int i=1;i<=n;i++){
if(l[i] >= m) break;
int cur = i, temp = 1;
for(int j=19;j>=0;j--){
if(r[st[j][cur]]-m<l[i]){
temp += (1 << j);
cur = st[j][cur];
}
}
cur = st[0][cur];
temp++;
if(r[cur] - m >= l[i]) ans = min(ans, temp);
}
cout << (ans == inf ? -1 : ans) << '\n';
#ifdef local
CHECK();
#endif
}
/*
input:
dp[i] =
*/
#ifdef local
void CHECK(){
cerr << "\n[Time]: " << 1000.0 * clock() / CLOCKS_PER_SEC << " ms.\n";
function<bool(string,string)> compareFiles = [](string p1, string p2)->bool {
std::ifstream file1(p1);
std::ifstream file2(p2);
if (!file1.is_open() || !file2.is_open())return false;
std::string line1, line2;
while (getline(file1, line1) && getline(file2, line2)) {
if (line1 != line2)return false;
}
int cnta=0,cntb=0;
while(getline(file1,line1))cnta++;
while(getline(file2,line2))cntb++;
return cntb-cnta<=1;
};
bool check = compareFiles("output.txt","expected.txt");
if (check) cerr<<"ACCEPTED\n";
else cerr<<"WRONG ANSWER!\n";
}
#else
#endif
