#include <bits/stdc++.h>

using namespace std;

#define int long long
#define ll long long
#define forn(i, n) for (ll i = 0; i < n; ++i)
#define forr(i, s, n) for (ll i = s; i < n; ++i)
#define fori(i, s, n) for (ll i = s; i > n; --i)
#define fora(i, n) for (auto i: n)
#define vi vector<int>
#define vll vector<ll>

const int MOD = 998244353;
// const int MOD = 1e9 + 7;

vector<tuple<int, bool, int>> points;
unordered_map<int,int> segPar;
vector<int> dist;
vector<int> prefsum;

void solve() {
    int n,k;
    cin >> n >> k;
    forn(i, n){
        int a,b;
        cin >> a >> b;
        points.push_back({a,false,i+1});
        points.push_back({b,true,i+1});
    }
    sort(points.begin(), points.end());

    // for (int i = 0;i < points.size();i++){
    //     cout << get<0>(points[i])<< " " << get<1>(points[i]) <<" " << get<2>(points[i]);
    //     cout << endl;
    // }
    // cout << endl;

    int curPar = -1;
    int active = 0;
    for (int i = 0;i < points.size();i++){
        auto& p = points[i];
        if (get<1>(p) == 0){
            if (curPar == -1){
                curPar = dist.size();
            }
            segPar[get<2>(p)] = curPar;
            active++;
        } else {
            active--;
            if (active == 0) {
                curPar = -1;
                if (i != points.size()-1){
                    dist.push_back(get<0>(points[i+1])-get<0>(p));
                }
            }
        }
    }
    prefsum.resize(dist.size());
    forn(i, prefsum.size()){
        prefsum[i] = dist[i];
        if (i != 0) prefsum[i] += prefsum[i-1];
    }

    // for (int i = 0;i < prefsum.size();i++){
    //     cout << prefsum[i] << " ";
    // }
    // cout << endl;

    int res = 0;
    int now = 1;
    forn(i,k){
        int next;
        cin >> next;
        int parA = segPar[now];
        int parB = segPar[next];
        now = next;
        if (parA == parB) continue;
        if (parA > parB) swap(parA,parB);
        // cout << parA << " " << parB << endl;
        res += prefsum[parB-1]-(parA == 0 ? 0 : prefsum[parA-1]);
    }   
    cout << res << endl;
}

int32_t main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    int t = 1;
    // cin >> t;
    while (t--) solve();

    return 0;
}