#include <bits/stdc++.h>
#define int long long
using namespace std;
typedef array<int, 2> pr;
const int MAX = 200001;
const int MAX_LOG = 20;
int A[MAX], B[MAX], sparse[MAX][MAX_LOG];
bool chk[MAX];
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
int N, M, K, X, ans = MAX;
vector<pr> arr;
priority_queue<pr> pq;
cin >> N >> M;
for (int i = 1; i <= N; i++) {
cin >> A[i] >> B[i];
if (A[i] <= B[i])
arr.push_back({A[i], -i}), arr.push_back({B[i], i});
else
arr.push_back({A[i], -i}), B[i] += M;
}
sort(arr.begin(), arr.end()), chk[0] = true;
for (pr i : arr) {
if (i[1] < 0)
pq.push({B[-i[1]], -i[1]});
else {
chk[i[1]] = true;
while (!pq.empty() && chk[pq.top()[1]])
pq.pop();
if (!pq.empty())
sparse[i[1]][0] = pq.top()[1];
}
}
for (int i = 1; i < MAX_LOG; i++)
for (int j = 1; j <= N; j++)
sparse[j][i] = sparse[sparse[j][i - 1]][i - 1];
for (int i = 1; i <= N; i++) {
if (B[i] >= M)
B[i] -= M;
}
for (int i = 1; i <= N; i++) {
if (!chk[i])
continue;
K = i, X = 1;
for (int j = MAX_LOG - 1; j >= 0; j--) {
if (sparse[K][j] == 0)
continue;
if (B[sparse[K][j]] >= B[i])
X += (1 << j), K = sparse[K][j];
}
if (B[sparse[K][0]] >= A[i] && !chk[sparse[K][0]])
ans = min(ans, X + 1);
}
cout << (ans == MAX ? -1 : ans) << '\n';
return 0;
}
