#include<bits/stdc++.h>

#define int long long
#define pb push_back
#define fi first
#define se second
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxN = 1e6 + 5;
const int mod = 1e9 + 7;
const ll oo = 1e18;
int n, k;
pair<int, int> a[maxN];
int b[maxN];
vector<pair<int, int>> adj[maxN];
void ReadInput()
{
    cin >> n >> k;
    for(int i=1; i<=n; i++)
        cin >> a[i].fi >> a[i].se;
    for(int i=1; i<=k; i++)
        cin >> b[i];
}
int jump[maxN][21];
int depth[maxN];
int f[maxN];
void dfs(int u, int par)
{
    for(auto [v, w] : adj[u])
    {
        if(v == par) continue;
        depth[v] = depth[u] + 1;
        f[v] = f[u] + w;
        jump[v][0] = u;
        for(int i=1; i<=18; i++)
            jump[v][i] = jump[jump[v][i - 1]][i - 1];
        dfs(v, u);
    }
}
int lca(int u, int v)
{
    if(depth[u] < depth[v]) swap(u, v);
    int k = depth[u] - depth[v];
    for(int i=18; i>=0; i--)
        if(k >> i & 1) u = jump[u][i];
    if(u == v) return u;
    for(int i=18; i>=0; i--)
        if(jump[u][i] != jump[v][i])
    {
        u = jump[u][i];
        v = jump[v][i];
    }
    return jump[u][0];
}
int dist(int u, int v)
{
    return f[u] + f[v] - 2 * f[lca(u, v)];
}
void Solve()
{
    int id = 1;
    for(int i=2; i<=n; i++)
    {
        adj[id].pb({i, max(0ll, a[i].fi - a[id].se)});
        adj[i].pb({id, max(0ll, a[i].fi - a[id].se)});
        if(a[i].se > a[id].se) id = i;
    }
    dfs(1, 0);
    b[0] = 1;
    int res = 0;
    for(int i=1; i<=k; i++)
        res += dist(b[i - 1], b[i]);
    cout << res;
}
#define taskname "sol"
int32_t main()
{
    if (fopen(taskname ".inp", "r"))
    {
        freopen(taskname ".inp", "r", stdin);
        //freopen(taskname ".out", "w", stdout);
    }
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    //cin >> T;
    for(int itest=1; itest<=T; itest++)
    {
        ReadInput();
        Solve();
    }
}