#include <bits/stdc++.h>

using namespace std;
// t1
#define gc _getchar_nolock
#define pii pair<long long, long long>
using ll = long long;
using cd = complex<double>;

const ll maxN = 7e4 + 10, maxM = 64 + 10, MAX = 2e6 + 10;
//const ll maxScore = 4294967295;
const ll mod = 999999999999999989;
const double pi = acos(-1.0);
const double PI = acos(-1.0);
const double e = exp(1.0);
const ll naught = -100001;
const ll maxT = ceil(sqrt(maxN)) + 1;
const ll root_rec = 15311432;
const ll root_1 = 469870224;
const ll root_pw = (1 << 23);
const int K = 20;
const int g = 3;
const int LOGN = 20;
const int num1 = 16;
const int INF = 1e9;
//const ll is_query = -(1LL<<62)



template <typename T> void fastInt(T& angka) {
    T kali = 1; angka = 0; char input = gc();
    while (!isdigit(input)) { if (input == '-') kali = -1; input = gc(); }
    while (isdigit(input)) angka = (angka << 3) + (angka << 1) + input - 48, input = gc();
    angka *= kali;
}

void fastStr(string& str) {
    str = "";
    char c = '0';
    while ((c = gc()) && (c != -1 && c != '\n' && c != '\t' && c != '\r' && c != ' ')) {
        str += c;
    }
}

ll powMod(ll x, ll y, ll p){
    ll res = 1;
    x %= p;
    if(!x) return 0;
    while (y > 0){
        if (y & 1) res = ((res % p) * (x % p)) % p;
        y = y >> 1;
        x = ((x % p) * (x % p)) % p;
    }
    return res;
}

ll inverseMod(ll x, ll p){
    return powMod(x, p - 2, p);
}

/*void upd(ll ind, ll l, ll r, ll i, ll val){
    if(l > r) return;
    if(i < l || r < i) return;
    if(l == r){
        assert(l == i);
        seg[ind] = val;
        return;
    }
    ll mid = (l + r) >> 1;
    upd(ind << 1, l, mid, i, val);
    upd(ind << 1 | 1, mid + 1, r, i, val);
    seg[ind] = max(seg[ind << 1], seg[ind << 1 | 1]);
}

ll query(ll ind, ll l, ll r, ll tl, ll tr){
    if(l > r) return 0;
    if(tr < l || r < tl) return 0;
    if(tl <= l && r <= tr) return seg[ind];
    ll mid = (l + r) >> 1;
    return max(query(ind << 1, l, mid, tl, tr), query(ind << 1 | 1, mid + 1, r, tl, tr));
}*/

void solve(){
    ll n, q;
    fastInt(n); fastInt(q);
    vector<pii> arr(n);
    vector<ll> uwu(n);
    vector<pii> compr;
    for(auto &x: arr){
        fastInt(x.first);
        fastInt(x.second);
    }
    ll r = arr[0].second, l = arr[0].first;
    ll cnt = 0;
    for(int i = 0; i < n; i++){
        if(arr[i].first <= r){
            r = max(r, arr[i].second);
            uwu[i] = cnt;
        }else{
            cnt++;
            uwu[i] = cnt;
            compr.push_back({l, r});
            l = arr[i].first;
            r = arr[i].second;
        }
    }
    compr.push_back({l, r});
    vector<ll> dp(compr.size());
    dp[0] = 0;
    for(int i = 1; i < compr.size(); i++){
        dp[i] = dp[i - 1] + compr[i].first - compr[i - 1].second;
        //cout << dp[i] << " ";
    }
    //cout << endl;
    vector<ll> que(q + 1);
    que[0] = 1;
    for(int i = 1; i < q + 1; i++){
        fastInt(que[i]);
    }
    ll ans = 0;
    for(int i = 0; i < q; i++){
        int l = min(uwu[que[i] - 1], uwu[que[i + 1] - 1]);
        int r = max(uwu[que[i] - 1], uwu[que[i + 1] - 1]);
        //cout << l << " " << r << " " << que[i] << endl;
        ans += dp[r] - dp[l];
    }
    cout << ans << '\n';
}

int32_t main(){
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cout.precision(10);
    //auto beg = high_resolution_clock::now();
    //cout << req(1e7 + 8) << '\n';
    int t; t = 1;
    while(t--) solve();
    //auto en = high_resolution_clock::now();
    //auto dur = duration_cast<microseconds>(en - beg);
    //cout << dur.count() << endl;
    return 0;
}

answer.code: In function ‘void fastInt(T&)’:
answer.code:6:12: error: there are no arguments to ‘_getchar_nolock’ that depend on a template parameter, so a declaration of ‘_getchar_nolock’ must be available [-fpermissive]
    6 | #define gc _getchar_nolock
      |            ^~~~~~~~~~~~~~~
answer.code:32:41: note: in expansion of macro ‘gc’
   32 |     T kali = 1; angka = 0; char input = gc();
      |                                         ^~
answer.code:6:12: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)
    6 | #define gc _getchar_nolock
      |            ^~~~~~~~~~~~~~~
answer.code:32:41: note: in expansion of macro ‘gc’
   32 |     T kali = 1; angka = 0; char input = gc();
      |                                         ^~
answer.code:6:12: error: there are no arguments to ‘_getchar_nolock’ that depend on a template parameter, so a declaration of ‘_getchar_nolock’ must be available [-fpermissive]
    6 | #define gc _getchar_nolock
      |            ^~~~~~~~~~~~~~~
answer.code:33:68: note: in expansion of macro ‘gc’
   33 |     while (!isdigit(input)) { if (input == '-') kali = -1; input = gc(); }
      |                                                                    ^~
answer.code:6:12: error: there are no arguments to ‘_getchar_nolock’ that depend on a template parameter, so a declaration of ‘_getchar_nolock’ must be available [-fpermissive]
    6 | #define gc _getchar_nolock
      |            ^~~~~~~~~~~~~~~
answer.code:34:86: note: in expansion of macro ‘gc’
   34 |     while (isdigit(input)) angka = (angka << 3) + (angka << 1) + input - 48, input = gc();
      |                                                                                      ^~
answer.code: In function ‘void fastStr(std::string&)’:
answer.code:6:12: error: ‘_getchar_nolock’ was not declared in this scope; did you mean ‘getchar_unlocked’?
    6 | #define gc _getchar_nolock
      |            ^~~~~~~~~~~~~~~
answer.code:41:17: note: in expansion of macro ‘gc’
   41 |     while ((c = gc()) && (c != -1 && c != '\n' && c != '\t' && c != '\r' && c != ' ')) {
      |                 ^~
answer.code: In instantiation of ‘void fastInt(T&) [with T = long long int]’:
answer.code:86:12:   required from here
answer.code:32:43: error: ‘_getchar_nolock’ was not declared in this scope; did you mean ‘getchar_unlocked’?
   32 |     T kali = 1; angka = 0; char input = gc();
      |                                           ^