#include <bits/stdc++.h>
using namespace std;

int main(){
    int n, x;
    cin >> n >> x;
    int ml = -1;
    int mr = 1001;
    for(int i = 0; i < n; i++){
        int l, r;
        cin >> l >> r;
        if (l > r) swap(l, r);
        ml = max(ml, l);
        mr = min(mr, r);
    }
    if(ml > mr){
        cout << -1;
    }else{
        int a = -1;
        if(x < ml){
            a = ml;
        }else if(x > mr){
            a = mr;
        }else{
            a = x;
        }
        cout << abs(a - x);
    }
    return 0;
}