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

using i64 = long long;

const int N = 1e5 + 10;

int n, k;
i64 a[N];

bool check(i64 m) {
    i64 tot = 0;
    int rk = k;
    for(int i = 1; i <= n; i ++) {
        if(tot + a[i] >= m) continue;
        if((m - tot - a[i] + i - 1) / i > rk) return false;
        rk -= (m - tot - a[i] + i - 1) / i;
        tot += ((m - tot - a[i] + i - 1) / i) * i;
    }
    return true;
}

int main() {
    cin >> n >> k;
    for(int i = 1; i <= n; i ++)
        cin >> a[i];
    
    i64 l = 0, r = 3e14;
    while(l + 1 < r) {
        i64 mid = (l + r) / 2;
        if(check(mid)) l = mid;
        else r = mid;
    }
    cout << l;
}