fn main() {
    input! {
        n: usize,
        k: i64,
        a: [i64; n],
    }
    let can = |mid: i64| -> bool {
        let mut add = 0;
        let mut cnt = 0;
        for (i, a) in a.iter().enumerate() {
            let i = i as i64 + 1;
            let need = (mid - add - *a).max(0);
            cnt += (need + i - 1) / i;
            add += (need + i - 1) / i * i;
        }
        cnt <= k
    };
    let mut ok = 0;
    let mut ng = 1;
    while can(ng) {
        ok = ng;
        ng *= 2;
    }
    while ng - ok > 1 {
        let mid = (ok + ng) / 2;
        if can(mid) {
            ok = mid;
        } else {
            ng = mid;
        }
    }
    println!("{}", ok);
}

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------