#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fti(i, x, y) for (int i = x; i <= y; ++i)
#define ftd(i, x, y) for (int i = x; i >= y; --i)
#define F first
#define S second
int n, m, res = 200005, lg;
pair <int, int> t[200005];
bool gr[200005];
int s[200005], e[200005], up[200005][20];
int tree[800005];
int get(int x, int y)
{
return (t[x].S < t[y].S ? y : x);
}
void build(int nd = 1, int l = 1, int r = n)
{
if (l == r)
{
tree[nd] = l; return;
}
int c = (l + r) >> 1, p1 = nd << 1, p2 = p1 | 1;
build(p1, l, c); build(p2, c + 1, r);
tree[nd] = get(tree[p1], tree[p2]);
}
int query(int L, int R, int nd = 1, int l = 1, int r = n)
{
if (r < L || R < l) return 0;
if (L <= l && r <= R) return tree[nd];
int c = (l + r) >> 1, p1 = nd << 1, p2 = p1 | 1;
return get(query(L, R, p1, l, c), query(L, R, p2, c + 1, r));
}
void sus2()
{
build();
fti(i, 1, n)
{
pair <int, int> nxt = {t[i].S + 1, 0};
int pos = lower_bound(t + 1, t + n + 1, nxt) - t - 1;
up[i][0] = query(1, pos);
}
lg = __lg(n);
fti(j, 1, lg)
fti(i, 1, n)
up[i][j] = up[up[i][j - 1]][j - 1];
fti(i, 1, n)
{
int l = t[i].F, cur = i, cnt = 1;
ftd(j, 19, 0)
{
int r = t[up[cur][j]].S;
if (r && r - l + 1 <= m)
cur = up[cur][j], cnt += (1 << j);
}
int r = t[up[cur][0]].S;
if (r - l + 1 > m)
res = min(res, cnt + 1);
}
cout << (res > n ? -1 : res);
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> m;
fti(i, 1, n)
{
cin >> t[i].F >> t[i].S;
if (t[i].F > t[i].S) t[i].S += m;
}
sort(t + 1, t + 1 + n);
sus2();
return 0;
}
