#include <bits/stdc++.h>
using namespace std;
const int N = 2e5 + 100, LG = 18;
int n, m, mx[N][LG], par[N][LG];
vector<pair<int, int>> vec;
int get_max(int l, int r){
int lg = 31 - __builtin_clz(r - l + 1);
if (vec[mx[l][lg]].second > vec[mx[r - (1 << lg) + 1][lg]].second)
return mx[l][lg];
return mx[r - (1 << lg) + 1][lg];
}
int main(){
int n, m;
cin >> n >> m;
for (int i = 0; i < n; i ++){
int l, r;
cin >> l >> r;
if (r < l) r += m;
vec.push_back({l, r});
}
sort(vec.begin(), vec.end());
for (int i = n - 1; i >= 0; i --){
mx[i][0] = i;
for (int j = 1; j < LG; j ++){
mx[i][j] = mx[i][j - 1];
if (i + (1 << (j - 1)) < n){
if (vec[ mx[i + (1 << (j - 1))][j - 1] ].second > vec[mx[i][j]].second)
mx[i][j] = mx[i + (1 << (j - 1))][j - 1];
}
}
}
for (int i = 0; i < n; i ++){
auto [l, r] = vec[i];
int j = upper_bound(vec.begin(), vec.end(), (pair<int,int>){r+1,-1}) - vec.begin();
j--;
par[i][0] = get_max(i, j);
// cout << vec[i].first << " " << vec[i].second << " -- " << vec[par[i][0]].first << " " << vec[par[i][0]].second << endl;
}
for (int i = 0; i < n; i ++)
for (int j = 1; j < LG; j ++)
par[i][j] = par[par[i][j - 1]][j - 1];
int ans = -1;
for (int i = 0; i < n; i ++){
int cur = i;
int steps = 1;
// cout << "----" << endl;
// cout << vec[i].first << " " << vec[i].second << endl;
for (int j = LG - 1; j >= 0; j --){
if (par[cur][j] != cur and vec[par[cur][j]].second < vec[i].first + m){
cur = par[cur][j];
steps += 1 << j;
// cout << vec[cur].first << " -" << j << "- " << vec[cur].second << endl;
}
}
// cout << i << " " << steps << endl;
if (vec[par[cur][0]].second >= vec[i].first + m)
steps++;
else
steps = -1;
if (steps == -1) continue;
if (ans == -1 or ans > steps) ans = steps;
}
cout << ans << endl;
}
