#include <iostream>
#include <vector>
#include <deque>
#include <set>
#include <queue>
#include <string>
#include <limits>
#include <map>
#include <algorithm>
#include <stack>

using namespace std;
using ll = long long int;
const ll mod = 1e9 + 7;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<int> v(n);
  for(auto& i : v)
    cin >> i;
  vector<int> munka(m);
  for(auto&i : munka){
    cin >> i;
  }
  sort(begin(munka), end(munka));
  int sol = 0, ptr = 0;
  for(int i = 0; i < n; ++i){
    while(ptr < m && munka[ptr] < i + 1) ++ptr;
    sol += min(m - ptr, v[i]);
    ptr += min(m - ptr, v[i]);
  }
  cout << sol << endl;
}