use std::io::Write;
use std::collections::*;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;

fn main() {
    input! {
        n: usize,
        l: i64,
        k: usize,
        a: [i64; n],
    }
    let mut a = a;
    a.push(l);
    a.insert(0, 0);
    let can = |m: i64| -> bool {
        let mut next = vec![a.len(); a.len()];
        let mut r = a.len() - 1;
        for i in (0..a.len()).rev() {
            while a[r - 1] - a[i] >= m {
                r -= 1;
            }
            if a[r] - a[i] >= m {
                next[i] = r;
            }
        }
        let mut dp = vec![0; a.len()];
        for j in 0..3 {
            let mut ndp = vec![a.len(); a.len()];
            for i in 0..(dp.len() - 1) {
                let v = dp[i];
                dp[i + 1].chmin(v);
                if next[i] < a.len() {
                    ndp[next[i]].chmin(v + next[i] - i - 1);
                }
            }
            if j < 2 {
                dp = ndp;
            }
        }
        dp[a.len() - 1] <= n - k
    };
    let mut ok = 1;
    let mut ng = l + 1;
    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 ----------
// ---------- begin chmin, chmax ----------
pub trait ChangeMinMax {
    fn chmin(&mut self, x: Self) -> bool;
    fn chmax(&mut self, x: Self) -> bool;
}

impl<T: PartialOrd> ChangeMinMax for T {
    fn chmin(&mut self, x: Self) -> bool {
        *self > x && {
            *self = x;
            true
        }
    }
    fn chmax(&mut self, x: Self) -> bool {
        *self < x && {
            *self = x;
            true
        }
    }
}
// ---------- end chmin, chmax ----------