#include <bits/stdc++.h>
using namespace std;
#define varazssor ios_base::sync_with_stdio(0); cin.tie(0);
using ll = long long;

//2.
int main(){
    varazssor;
    int n, m; cin >> n >> m;
    vector <int> rend(n); //nap
    vector <int> osszrend(m); //határidő
    for(int i = 0; i < n; ++i){
        cin >> rend[i];
    }
    for(int i = 0; i < m; ++i){
        cin >> osszrend[i];
    }
    sort(osszrend.begin(), osszrend.end());

    int cnt = 0;
    for (int i = 0; i < n; ++i){
        int vege = rend[i];
        for (int j = 0; j < m; ++j){
            if (osszrend[j] >= i + 1 && vege > 0){
                cnt++;
                vege--;
            }
            if (vege == 0){break;}
        }
    }
    cout << cnt << '\n';
}