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

int main() {
    int N, M, rendelesek = 0;
    cin >> N >> M;

    vector<int> munkaora(N);
    vector<int> hatarido(M);

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

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

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


    /*
    3 5
    2 0 6
    1
    2
    2
    3
    3
    
    
    */




    for(int i = 0; i < N; i++){
        int munka = munkaora[i];
        if(munka == 0) continue;

        for(int j = 0; j < M; j++) {
            if(hatarido[j] >= i+1 && munka > 0 && hatarido[j] != -1) {
                rendelesek++;
                munka--;
                hatarido[j] = -1;
            } else {
                break;
            }
        }
       
    }


    
    cout << rendelesek;


    return 0;
}