//proconio
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let mut 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_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_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>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

fn main() {
    input!(n: usize, m: usize, D: [[i128; m]; n]);
    let mut memo = Vec::new();
    for i in 0..n {
        let mut temp = Vec::new();
        for j in 0..m {
            temp.push(D[i][j])
        }
        temp.sort();
        // println!("temp, {:?}", &temp);
        memo.push(temp);
    }
    // std::process::exit(0);
    let mut ok = 1000_000_000_0;
    let mut ng = -1;
    while ok - ng > 1 {
        let mid = (ok + ng) / 2;
        if check(mid, n, m, &memo) {
            ok = mid;
        } else {
            ng = mid;
        }
    }
    // eprintln!("ok {}", ok);
    // eprintln!("ng {}", ng);
    if ok > 1000_000_000 {
        ok = -1;
    }
    println!("{}", ok);
}

fn check(x: i128, n: usize, m: usize, memo: &Vec<Vec<i128>>) -> bool {
    // eprintln!("x {}", x);
    let mut res = false;
    let mut dp = vec![vec![false; m]; n];
    for j in 0..m {
        dp[0][j] = true;
    }
    for i in 0..n - 1 {
        let ni = i + 1;
        let mut left = 0;
        let mut right = 0;
        let mut flagnums = vec![0; m + 1];
        for j in 0..m {
            if !dp[i][j] {
                continue;
            }
            let preval = memo[i][j];
            while (left < m - 1) & (memo[ni][left] < preval) {
                left += 1;
            }

            // 遷移不可能
            if (left == m - 1) & (memo[ni][left] < preval) {
                break;
            }

            // right = right.max(left);
            while right < m {
                if memo[ni][right] <= preval + x {
                    right += 1;
                } else {
                    break;
                }
            }
            // eprintln!("i j left right {} {} {} {}", i, j, left, right);
            flagnums[left] += 1;
            flagnums[right] -= 1;
            // eprintln!("flag {:?}", flagnums);
        }

        for j in 0..m {
            flagnums[j + 1] += flagnums[j];
        }
        // eprintln!("flag {:?}", flagnums);

        for j in 0..m {
            if flagnums[j] > 0 {
                dp[ni][j] = true;
            }
        }
    }
    for j in 0..m {
        if dp[n - 1][j] {
            res = true;
            // eprintln!("hoge");
            break;
        }
    }
    res
}