#include <iostream>
#include <cmath>
#include <cstdlib>
using namespace std;


int min_element(int *nums){
    if (nums[0] > nums[1]) return nums[0];
    return nums[1];
}


int main(){
    long long int start;
    long long int olymp;
    long long int portals_qnt;
    cin>>start;
    cin>>olymp;
    cin>>portals_qnt;
    long long int lp_from_start = -pow(10, 8);
    long long int rp_from_start = pow(10, 8);
    long long int lp_from_olymp = -pow(10, 8);
    long long int rp_from_olymp = pow(10, 8);
    for (int i = 0; i < portals_qnt; i++){
        int portal_coord;
        cin>>portal_coord;
        if (portal_coord < olymp and portal_coord > lp_from_olymp) lp_from_olymp = portal_coord;
        else if (portal_coord >= olymp and portal_coord < rp_from_olymp) rp_from_olymp = portal_coord;
        if (portal_coord < start and portal_coord > lp_from_start) lp_from_start = portal_coord;
        else if (portal_coord >= start and portal_coord < rp_from_start) rp_from_start = portal_coord;
    }
    long long int &time_to_olymp_from_portal = *min_element({abs(rp_from_olymp - olymp), abs(olymp - lp_from_olymp)});
    long long int &time_to_start_from_portal = *min_element({abs(rp_from_start - start), abs(start - lp_from_start)});
    long long int time_through_portal = time_to_olymp_from_portal + time_to_start_from_portal + 1;
    long long int time_to_olymp_from_start = abs(start - olymp);
    long long int &res = *min_element({time_through_portal, time_to_olymp_from_start});
    cout<<res;
}