#include<bits/stdc++.h>
#define rep(i,s,n) for (int i = (int)(s); i < (int)(n); i++)
#define all(v) begin(v),end(v)
using namespace std;
using ll = long long;
bool chmin(auto &a, auto b){ return a > b ? a = b, 1 : 0; }
bool chmax(auto &a, auto b){ return a < b ? a = b, 1 : 0; }

using pii = pair<int,int>;

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v){
    const char* delim = "";
    for (auto &e : v){
        os << exchange(delim, " ") << e;
    }
    return os;
}

void solve(){
    int n; cin >> n;
    int k; cin >> k;
    vector<int> xs;
    vector<pii> lrs(n);
    rep(i,0,n){
        int l, r; cin >> l >> r;
        lrs[i] = {l,r};
        xs.emplace_back(l);
        xs.emplace_back(r);
    }
    sort(all(xs));
    xs.erase(unique(all(xs)),xs.end());
    auto id = [&](int raw){
        return lower_bound(all(xs),raw) - xs.begin();
    };
    int sz = xs.size();
    vector<int> imos(sz,0);
    rep(i,0,n){
        imos[id(lrs[i].first)]++;
        imos[id(lrs[i].second)]--;
    }
    rep(i,0,sz-1){
        imos[i+1] += imos[i];
    }
    vector<int> rui(sz,0);
    rep(i,0,sz-1){
        rui[i+1] = rui[i] + (imos[i] == 0 ? xs[i+1] - xs[i] : 0);
    }
    // cout << xs << endl;
    // cout << rui << endl;
    // cout << imos << endl;
    ll ans = 0;
    int cur = 0;
    rep(i,0,k){
        int nxt; cin >> nxt; nxt--;
        int ic = id(lrs[cur].first);
        int in = id(lrs[nxt].first);
        if (ic > in) swap(ic,in);
        // cout << in << ' ' << ic << endl;
        ans += rui[in] - rui[ic];
        cur = nxt;
    }
    cout << ans << '\n';
}

int main(){
    cin.tie(0)->sync_with_stdio(0);
    solve();
}