#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int n, m, kesz = 0, ans = 0;
vector <int> o(1e4 + 1);
vector <int> v;

int main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i++) cin >> o[i];
    v.resize(m);
    for (int& i : v) cin >> i;
    sort(v.begin(), v.end());
    for (int i = 1; i <= n; i++) {
        int h = lower_bound(v.begin(), v.end(), i) - v.begin();
        kesz = max(kesz, h);
        if (kesz + o[i] > m) { ans += m - kesz; break; }
        kesz += o[i];
        ans += o[i];
    }
    cout << ans;
}