Given a matrix (H × W) which contains only 1 and 0, find the area of the largest rectangle which only contains 0s.

Constraints

* 1 ≤ H, W ≤ 1,400

Input


H W
c1,1 c1,2 ... c1,W
c2,1 c2,2 ... c2,W
:
cH,1 cH,2 ... cH,W


In the first line, two integers H and W separated by a space character are given. In the following H lines, ci,j, elements of the H × W matrix, are given.

Output

Print the area (the number of 0s) of the largest rectangle.

Example

Input

4 5
0 0 1 0 0
1 0 0 0 0
0 0 0 1 0
0 0 0 1 0


Output

6
#include<bits/stdc++.h>
const static int MAX = 1400;

int H, W;
int buffer[MAX][MAX];
int T[MAX][MAX];

struct Rectangle{
    int height;
    int pos;
};

int getLargestRectangle(int size, int buffer[]){
    std::stack<Rectangle> S;
    int maxv = 0;
    buffer[size] = 0;

    for(int i = 0; i <= size; i++){
        Rectangle rect;
        rect.height = buffer[i];
        rect.pos = i;
        if( S.empty() ){
            S.push(rect);
        }else{
            if(S.top().height < rect.height){
                S.push(rect);
            }else if(S.top().height > rect.height){
                int target = i;
                while(!S.empty() && S.top().height >= rect.height){
                    Rectangle pre = S.top(); S.pop();
                    int area = pre.height * (i - pre.pos);
                    maxv = std::max(maxv, area);
                    target = pre.pos;
                }
                rect.pos = target;
                S.push(rect);
            }
        }
    }
    return maxv;
}


int getLargestRectangle(){
    for(int j = 0; j < W; j++){
        for(int i = 0; i < H; i++){
            if(buffer[i][j]){
                T[i][j] = 0;
            }else{
                T[i][j] = (i > 0) ? T[i-1][j] + 1 : 1;
            }
        }
    }

    int maxv = 0;
    for(int i = 0; i < H; i++){
        maxv = std::max( maxv, getLargestRectangle(W, T[i]) );
    }

    return maxv;
}

int main(void){

    scanf("%d %d", &H, &W);

    for(int i = 0; i < H; i++){
        for(int j = 0; j < W; j++){
            scanf("%d", &buffer[i][j]);
        }
    }
    std::cout << getLargestRectangle() << std::endl;

    return 0;
}
