#include <bits/stdc++.h>
using namespace std;
#define fast ios::sync_with_stdio(0);cin.tie(0);
typedef long long ll;
#define f first
#define s second
#define LOGN 20
const ll MOD = 1e9 + 7;
const ll MAXN = 8e5 + 100;
ll N, M;
int s[MAXN], e[MAXN], sg[4*MAXN], lazy[4*MAXN];
int up[LOGN][MAXN], mn = 1e7;
vector<int> cc;
void push(int k, int a, int b) {
if (lazy[k] != -1) {
sg[k] = max(sg[k], lazy[k]);
if (a != b) {
lazy[2*k] = max(lazy[2*k], lazy[k]);
lazy[2*k+1] = max(lazy[2*k+1], lazy[k]);
}
lazy[k] = -1;
}
}
void init(int k, int a, int b) {
if (a == b) {
sg[k] = a;
return ;
}
init(2*k, a, (a+b)/2);
init(2*k+1, (a+b)/2+1, b);
sg[k] = max(sg[2*k], sg[2*k+1]);
}
void update(int k, int a, int b, int q_l, int q_r, int val) {
push(k, a, b);
if (b < q_l || a > q_r)
return ;
if (q_l <= a && b <= q_r) {
lazy[k] = val;
push(k, a, b);
return ;
}
update(2*k, a, (a+b)/2, q_l, q_r, val);
update(2*k+1, (a+b)/2+1, b, q_l, q_r, val);
sg[k] = max(sg[2*k], sg[2*k+1]);
}
int query(int k, int a, int b, int plc) {
push(k, a, b);
if (b < plc || a > plc)
return 0;
if (a == b)
return sg[k];
return max(query(2*k, a, (a+b)/2, plc),
query(2*k+1, (a+b)/2+1, b, plc));
}
void try_i(int node) {
int now = node;
int x = 0;
for (int i = LOGN-1; i >= 0; i--) {
int y = up[i][now];
if (cc[y-1] < cc[node-1] + M) {
now = y;
x += (1<<i);
}
}
int y = up[0][now];
if (cc[y-1] >= cc[node-1] + M)
mn = min(mn, x + 1);
}
int main() {
fast
cin >> N >> M;
for (int i = 1; i <= N; i++) {
cin >> s[i] >> e[i];
cc.push_back(s[i]);
cc.push_back(e[i]);
cc.push_back(s[i] + M);
cc.push_back(e[i] + M);
}
sort(cc.begin(), cc.end());
cc.erase(unique(cc.begin(), cc.end()), cc.end());
int n = cc.size();
init(1, 0, n);
for (int i = 1; i <= N; i++) {
if (s[i] <= e[i]) {
int x1 = upper_bound(cc.begin(), cc.end(), s[i]) - cc.begin();
int x2 = upper_bound(cc.begin(), cc.end(), e[i]) - cc.begin();
int y1 = upper_bound(cc.begin(), cc.end(), s[i] + M) - cc.begin();
int y2 = upper_bound(cc.begin(), cc.end(), e[i] + M) - cc.begin();
update(1, 0, n, x1, x2, x2);
update(1, 0, n, y1, y2, y2);
} else {
int x1 = upper_bound(cc.begin(), cc.end(), s[i]) - cc.begin();
int x2 = upper_bound(cc.begin(), cc.end(), e[i] + M) - cc.begin();
update(1, 0, n, x1, x2, x2);
}
}
for (int i = 1; i <= n; i++)
up[0][i] = query(1, 0, n, i);
for (int i = 1; i < LOGN; i++) {
for (int j = 1; j <= n; j++)
up[i][j] = up[i-1][up[i-1][j]];
}
for (int i = 1; i <= n; i++)
try_i(i);
if (mn == 1e7)
mn = -1;
cout << mn << "\n";
}
