#include <bits/stdc++.h>
using namespace std;
int main(int argc, char** argv) {
  int n, x, p, min = 0, max = 1000;
  cin >> n >> x;
  p = x;
  for (int i = 0; i < n; i++) {
    int a, b;
    cin >> a >> b;
    if (a < b) {
      if ((p >= a) && (p <= b)) {
        if (a > min) min = a;
        if (b < max) max = b;
      } else if (p < a) {
        if (a <= max) {
          p = a;
          if (a > min) min = a;
          if (b < max) max = b;
        } else {
          cout << -1;
          return 0;
        }
      } else if (p > b) {
        if (b >= min) {
          p = b;
          if (a > min) min = a;
          if (b < max) max = b;
        } else {
          cout << -1;
          return 0;
        }
      }
    } else {
      if ((p >= b) && (p <= a)) {
        if (b > min) min = b;
        if (a < max) max = a;
      } else if (p < b) {
        if (b <= max) {
          p = b;
          if (b > min) min = b;
          if (a < max) max = a;
        } else {
          cout << -1;
          return 0;
        }
      } else if (p > a) {
        if (a >= min) {
          p = a;
          if (b > min) min = b;
          if (a < max) max = a;
        } else {
          cout << -1;
          return 0;
        }
      }
    }
  }
  if ((p - x) >= 0)
    cout << p - x;
  else
    cout << x - p;
  return 0;
}
