#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>
#include <iomanip>

using ll = long long;
using namespace std;

int main()
{
    int munkaorakSzama, hataridokSzama;
    cin >> munkaorakSzama >> hataridokSzama;

    vector<int> munkaorak(munkaorakSzama);
    vector<int> hataridok(hataridokSzama);

    for (int i = 0; i < munkaorakSzama; i++) {
        cin >> munkaorak[i];
    }

    for (int i = 0; i < hataridokSzama; i++) {
        cin >> hataridok[i];
    }

    sort(hataridok.begin(), hataridok.end());

    int jelenlegiOra = 1;
    int kesz = 0;
    int curHI = 0;
    for (int i = 0; i < munkaorakSzama; i++) {
        for (int j = 0; j < munkaorak[i]; j++) {
            while (hataridok[curHI] < i) {
                curHI++;
            }
            kesz++;
            munkaorak[i]--;
            curHI++;
        }
    }
    cout << kesz;
}