#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9, MOD = 1e9 + 7, ohara = 1e6;
const long long LINF = 1e18;
long long int n, cnt = 0, ans = 0, a, b, c, d, cmp[ohara], cmpp, m, h, w, x, y,
                 sum[ohara], pos;
int dy[] = {1, 0, -1, 0};
int dx[] = {0, 1, 0, -1};
string alph("abcdefghijklmnopqrstuvwxyz"), s;
bool fl = true;
struct edge {
  int to, cost;
};
int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> c;
  for (long long int(i) = 0; (i) < (int)(n); (i)++) {
    cin >> a >> b;
    if (a > b) {
      pos = b;
      b = a;
      a = pos;
    }
    sum[a]++;
    sum[b + 1]--;
  }
  for (long long int i = (1); i < (9999); i++) {
    sum[i] += sum[i - 1];
  }
  for (long long int(i) = 0; (i) < (int)(9999); (i)++) {
    if (sum[i] == n) {
      cmp[cnt] = i;
      cnt++;
      fl = false;
    }
  }
  if (fl) {
    cout << (-1) << endl;
    return 0;
  }
  ans = INF;
  for (long long int(i) = 0; (i) < (int)(cnt); (i)++) {
    ans = min(ans, max(cmp[i], c) - min(cmp[i], c));
  }
  cout << (ans) << endl;
  return 0;
}
