#include<fstream>
using namespace std;
ifstream in("grupuri.in");
ofstream out("grupuri.out");
int v[100003];
int main()
{
    int n,i,k;
    long long s=0;
    bool ok=false;
    in>>k>>n;
    for(i=1;i<=n-k;i++)
	{
		in>>v[i];
		s+=v[i];
	}
	for(i=n-k+1;i<=n;i++)
	{
		in>>v[i];
	}
	for(i=n-k+1;i<n&&s>0;i++)
	{
		if(s/(i-n+k)>v[i+1]-v[i])
			s-=(v[i+1]-v[i])*(i-n+k);
		else
			out<<v[i]+s/(i-n+k),s=0,ok=true;
	}
	if(s>0)
		out<<v[n]+s/k,ok=true;
	if(ok==false)
		out<<0;
    return 0;
}