#include <bits/stdc++.h>
#include <vector>
#include <algorithm>
#include <iostream>
#include <iterator>
#include <sstream>

using namespace std;

vector<int> readline()
{
    string input;
    getline(cin, input);
    vector<int> numbers;
    istringstream stream(input);
    int number;
    while (stream >> number)
        numbers.push_back(number);
    return numbers;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    auto templine = readline();

    int N = templine[0];
    int M = templine[1];
    auto T = readline();

    priority_queue<int, std::vector<int>, std::greater<int>> jobs;
    for(int i = 0;i<M;i++)
      jobs.push(readline()[0]);
    int f = 0;
    for(int i = 0;i<N;i++)
      {
        int m = T[i];
        int c = 0;
        while(c < m && !jobs.empty())
          {
            int j = jobs.top();
            jobs.pop();
            if(j - 1 < i)
              continue;
            f++;
            c++;
          }
      }
    cout << f;
  
    return 0;
}