#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fi("grupuri.in");
ofstream fo("grupuri.out");
int v[100002],n,k;

int main()
{
    fi>>k>>n;
    for (int i=1;i<=n;i++)
        fi>>v[i];
    int nr=0;
    while (v[n-k+1]!=0) {
        nr++;
        int x=v[n-k+1];
        for (int i=n-k+1;i<=n;i++)
            v[i]=v[i]-1;
        sort(v,v+n+1);
    }
    fo<<nr;
    return 0;
}