#include<bits/stdc++.h>
using namespace std;
using ll = long long;
ll n,k;
vector<ll> a;
bool is(ll m){
	ll cur = 0;
	ll cnt = 0;
	for(ll i = 0;i<n;i++){
		if(a[i]+cur<m){
			ll x  = m-(a[i]+cur);
			ll y = (x+i)/(i+1);
			cnt += y;
			cur += (i+1)*y;
		}
	}
	return cnt<=k;
}

void solve(){
	ll l = 0,r = 1e18;
	while(r-l>1){
		ll mid = (l+r)/2;
		if(is(mid)){
			l = mid;
		}else{
			r = mid;
		}
	}
	cout<<l<<endl;
}

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cin >> n >> k;
	a = vector<ll>(n);
	for(auto &i:a)cin >> i;
	solve();
}