#include <iostream>
#include <algorithm>
#define int long long
using namespace std;

struct Interval
{
    int s, e;
    int idx;
};

bool cmp(Interval i1, Interval i2)
{
    return i1.s < i2.s;
}

int loc[100005];
int cnt[100005];
int dis[100005];
int N, K;
Interval val[100005];

signed main()
{
    ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    cin >> N >> K;
    for (int i = 1; i <= N; i++) {
        cin >> val[i].s >> val[i].e;
        val[i].idx = i;
    }
    sort(val + 1, val + N + 1, cmp);
    int mx = -1, phase = 0;
    for (int i = 1; i <= N; i++) {
        if (mx < val[i].s) {
            dis[phase] = val[i].s - mx;
            phase++;
        }
        mx = max(mx, val[i].e);
        loc[val[i].idx] = phase;
    }
    //dis[i]: group i ~ group i+1 distance
    int prv; cin >> prv;
    for (int i = 2; i <= K; i++) {
        int x; cin >> x;
        if (loc[prv] < loc[x]) {
            cnt[loc[prv]]++;
            cnt[loc[x]]--;
        }
        else if (loc[prv] > loc[x]) {
            cnt[loc[x]]++;
            cnt[loc[prv]]--;
        }
        prv = x;
    }
    for (int i = 2; i <= phase-1; i++) cnt[i] += cnt[i-1];
    int ans = 0;
    for (int i = 1; i <= phase-1; i++) {
        ans += cnt[i] * dis[i];
    }
    cout << ans << '\n';
    return 0;
}