C++ :

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<vector>
#include<queue>
#include<map>
using namespace std;
const long long N=100+5;
long long a,n,p[N],gs,v[N],tmp[N],t;
int main()
{
	cin>>a>>n;
	for (int i=1;i<=n;i++) cin>>p[i];
	gs=n;
	while (1)
	{
		sort(p+1,p+gs+1);
		t=0;
		for (int i=1;i<=n;i++) v[i]=0,tmp[i]=0;
		for (long long i=1;i<=gs;i++) 
		{
			if (v[i]) continue;
			if (i+a-1>gs) { tmp[++t]=p[i]; continue; }
			if (p[i]!=p[i+a-1]) { tmp[++t]=p[i]; continue; }
			tmp[++t]=p[i]+1;
			for (int j=i;j<=i+a-1;j++) v[j]=1;
		}
		if (gs==t) break; gs=t;
		for (int i=1;i<=gs;i++) p[i]=tmp[i];
	}
	if (gs==1) cout<<p[gs]<<endl; else cout<<p[gs]+1<<endl;
	return 0;
}