#include <bits/stdc++.h>
using namespace std;
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    const int inf = 1e9 + 5;
    int n, m;
    cin >> n >> m;
    vector<int> a(n + 2), b(m);
    for(int i = 1; i <= n; i++) cin >> a[i];
    a[n + 1] = inf;
    for(int j = 0; j < m; j++) cin >> b[j];
    sort(b.begin(), b.end());
    vector<int> dp(n + 2);
    set<array<int, 3> > s;
    s.insert({0, 0});
    for(int i = 1; i <= n + 1; i++)
    {
        int ind = lower_bound(b.begin(), b.end(), a[i]) - b.begin();
        int val = a[i] - i + 1;
        auto it = s.lower_bound({val, a[i], -inf});
        if(it == s.begin())
        {
            dp[i] = n + 1;
            continue;
        }
        it--;
        dp[i] = (*it)[2] + i - 1;
        //cout << i << " " << dp[i] << " " << val << " " << it -> first << " " << it -> second << "\n";
        int ins = a[i] - i, ival = dp[i] - i;
        while(1)
        {
            auto it2 = s.lower_bound({ins, a[i], -inf});
            if(it2 != s.end() && (*it2)[2] >= ival) s.erase(it2);
            else break;
        }
        s.insert({ins, a[i], ival});

    }
    cout << dp[n + 1] << "\n";
}