#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001

int main(){
	
	long long N,K;
	cin>>N>>K;
	vector<long long> a(N);
	rep(i,N){
		cin>>a[i];
		
	}
	long long ok = 0,ng = 1000000000000000;
	while(ng-ok>1LL){
		long long mid = (ok+ng)/2;
		
		long long cnt = 0,sum = 0;
		bool f = true;
		rep(i,N){
			if(cnt > K)break;
			if(sum >= mid)break;
			long long ca = a[i] + sum;
			if(ca>=mid)continue;
			ca = mid - ca;
			long long t = i+1;
			cnt += (ca+t-1) / t;
			sum += ((ca+t-1) / t) * t;
		}
		if(cnt <= K)ok = mid;
		else ng = mid;
		
	}
	cout<<ok<<endl;
	
	return 0;
}