#include <bits/stdc++.h>
using namespace std;

using ll = long long;

int main()
{
	ll n, k;
	cin >> n >> k;
	vector<ll> a(n);
	for(ll i = 0; i < n; i++) cin >> a[i];
	
	ll ok = 0;
	ll ng = 1000000000000000;
	ll mid;
	ll ck, cnt;
	while(abs(ok - ng) != 1)
	{
		mid = (ok + ng) / 2;
		ck = k;
		cnt = 0;
		for(ll i = 0; i < n; i++)
		{
			if(mid <= cnt + a[i]) continue;
			ck -= (mid - cnt - a[i] + i) / (i + 1);
			cnt += (i + 1) * ((mid - cnt - a[i] + i) / (i + 1));
		}
		
		if(ck < 0) ng = mid;
		else ok = mid;
	}
	cout << ok << endl;
	return 0;
}