#include <fstream>
#include <algorithm>
#define NM 1000005

using namespace std;

ifstream fin("grupuri.in");
ofstream fout("grupuri.out");

int n, k, i, s;
int v[NM], nr, sol;

int main()
{
    fin >> k >> n;
    for (i=1; i<=n; i++)
      fin >> v[i];
    while (n-nr>=k)
    {
        sol++;
        for (i=n; i>=n-k+1; i--)
        {
            if (v[i]==1)
              nr++;
            v[i]--;
        }
        sort(v+1, v+n+1);
    }
    fout << sol << " ";
    fin.close();
    fout.close();
    return 0;
}