// vallalkozo.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <queue>
#include <algorithm>
#define ll long long 
using namespace std;

ll n, m;
int main()
{
	
	cin >> n >> m;
	vector<ll>x(n + 1);
	deque<ll>munka(m);
	for (int i = 1; i <= n; ++i)
	{
		cin >> x[i];
	}
	for (int i = 1; i <= m; ++i)
	{
		cin >> munka[i - 1];
	}
	sort(munka.begin(), munka.end());
	int i = 1,db=0;
	while (!munka.empty())
	{
		while (!munka.empty()&& munka[0] >= i && x[i] != 0)
		{
			munka.pop_front();
			x[i]--;
			db++;
		}
		if (x[i] == 0)
		{
			while (munka[0] == i)munka.pop_front();
		}
		++i;
	}
	cout << db;
   return 0;
}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started: 
//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file