#include <bits/stdc++.h>
using namespace std;
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);
    int b, p;
    cin >> b >> p;
    vector<int> nums = vector<int>(p);
    for (int i = p-1; i >= 0; i--) {
        int v;
        cin >> v;
        nums[i] = v;
    }
    int res = INT_MAX;
    for (int z = 0; z < 2; z++) {
        vector<pair<int,int>> curr(1, {INT_MAX, 0});
        for (int i = 0; i < p; i++) {
            vector<pair<int,int>> nex((i+1)*b+1, {INT_MAX, INT_MAX});
            int v = nums[i];
            for (int j = 0; j <= i*b; j++) {
                // We have v+1, they have b-v-1
                int prevRec = curr[j].first;
                if (prevRec != INT_MAX) {
                    nex[j].first = min(nex[j].first, prevRec+(b-v-1));
                    nex[j+v+1].second = min(nex[j+v+1].second, prevRec);
                }

                // We have v, they have b-v
                int prevGiv = curr[j].second;
                if (prevGiv != INT_MAX) {
                    nex[j].first = min(nex[j].first, prevGiv+(b-v));
                    nex[j+v].second = min(nex[j+v].second, prevGiv);
                }
            }
            swap(curr, nex);
            // cout << z << " " << i << "!!\n";
            // for (int j = 0; j < curr.size(); j++) {
            //     if (curr[j].first != INT_MAX || curr[j].second != INT_MAX) {
            //         cout << j << " " << curr[j].first << " " << curr[j].second << "\n";
            //     }
            // }
        }
        for (int i = 0; i <= b * p; i++) {
            if (curr[i].first <= i || curr[i].second <= i) {
                res = min(res, i);
                break;
            }
        }
        if (z == 0) {
            for (int i = 0; i < p; i++)
            {
                nums[i] = b - nums[i] - 1;
            }
            nums[0]++;
        }
    }
    cout << res << '\n';
}

/*

50 5
45 45 45 45 45

50 5
5 5 5 5 5

50 5
5 5 45 45 5


*/