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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N,K;
    cin >> N >> K;
    vector<long long>A(N);
    for(int i = 0; i < N; i++) {
        cin >> A[i];
    }
    long long l = 0,r = 2001001001001001;
    while(l+1 < r) {
        long long mid = (l+r)/2;
        long long sum = 0,sum2 = 0;
        for(int i = 0; i < N; i++) {
            if(sum+A[i] <= mid) {
                sum2 += (mid-sum-A[i]+i)/(i+1);
                sum += (mid-sum-A[i]+i)/(i+1)*(i+1);
            }
        }
        if(sum2 <= K) {
            l = mid;
        }
        else {
            r = mid;
        }
    }
    cout << l << endl;
}