use std::cmp;
use std::collections::VecDeque;

trait TopQueue<T> {
    fn top(&self) -> &T;
}

impl<T> TopQueue<T> for VecDeque<T> {
    fn top(&self) -> &T {
        assert!(!self.is_empty());
        self.iter().next().unwrap()
    }
}

fn f(hist: &Vec<usize>) -> usize {
    let n = hist.len();
    let mut ans = 0;
    let mut q: VecDeque<(usize, usize)> = VecDeque::new();

    for i in 0..n {
        let mut reachable_min = i;
        while !q.is_empty() && q.top().1 > hist[i] {
            let (pos, height) = q.pop_front().unwrap();
            reachable_min = pos;
            ans = cmp::max(ans, (i - reachable_min) * height);
        }

        if q.is_empty() || q.top().1 < hist[i] {
            q.push_front((reachable_min, hist[i]));
        }
    }
    while !q.is_empty() {
        let (pos, height) = q.pop_front().unwrap();
        ans = cmp::max(ans, (n - pos) * height);
    }
    ans
}

fn main() {
    let mut sc = Scanner::new();
    let h = sc.read();
    let w = sc.read();
    let mut c = vec![vec![false; w]; h];
    for i in 0..h {
        for j in 0..w {
            c[i][j] = sc.read::<usize>() == 0;
        }
    }

    let mut hist = vec![vec![0; w]; h];
    for i in 0..h {
        for j in 0..w {
            if !c[i][j] {
                continue;
            }
            if i == 0 {
                hist[i][j] = 1;
            } else {
                hist[i][j] = hist[i - 1][j] + 1;
            }
        }
    }

    let mut ans = 0;
    for i in 0..h {
        ans = cmp::max(ans, f(&hist[i]));
    }
    println!("{}", ans);
}

struct Scanner {
    ptr: usize,
    length: usize,
    buf: Vec<u8>,
    small_cache: Vec<u8>,
}

#[allow(dead_code)]
impl Scanner {
    fn new() -> Scanner {
        Scanner {
            ptr: 0,
            length: 0,
            buf: vec![0; 1024],
            small_cache: vec![0; 1024],
        }
    }

    fn load(&mut self) {
        use std::io::Read;
        let mut s = std::io::stdin();
        self.length = s.read(&mut self.buf).unwrap();
    }

    fn byte(&mut self) -> u8 {
        if self.ptr >= self.length {
            self.ptr = 0;
            self.load();
            if self.length == 0 {
                self.buf[0] = b'\n';
                self.length = 1;
            }
        }

        self.ptr += 1;
        return self.buf[self.ptr - 1];
    }

    fn is_space(b: u8) -> bool {
        b == b'\n' || b == b'\r' || b == b'\t' || b == b' '
    }

    fn read_vec<T>(&mut self, n: usize) -> Vec<T>
    where
        T: std::str::FromStr,
        T::Err: std::fmt::Debug,
    {
        (0..n).map(|_| self.read()).collect()
    }

    fn usize_read(&mut self) -> usize {
        self.read()
    }

    fn read<T>(&mut self) -> T
    where
        T: std::str::FromStr,
        T::Err: std::fmt::Debug,
    {
        let mut b = self.byte();
        while Scanner::is_space(b) {
            b = self.byte();
        }

        for pos in 0..self.small_cache.len() {
            self.small_cache[pos] = b;
            b = self.byte();
            if Scanner::is_space(b) {
                return String::from_utf8_lossy(&self.small_cache[0..(pos + 1)])
                    .parse()
                    .unwrap();
            }
        }

        let mut v = self.small_cache.clone();
        while !Scanner::is_space(b) {
            v.push(b);
            b = self.byte();
        }
        return String::from_utf8_lossy(&v).parse().unwrap();
    }
}



Measured memory_bytes: 23360