const nm = gets();
numbers = nm.split(" ");
var n = numbers[0];
var m = numbers[1];
const arr = new Array(n);

for(let i = 0; i < n; i++) {
    arr[i] = new Array(m);
    for(let j = 0; j < m; j++) {
        arr[i][j] = +gets();
    }
}

var count = 1;
var max = 0;
var chislo = arr[1].length - 2;

for (let i = 0; i < arr.length; i++) {
    for (let j = 1; j < arr[i].length; j++) {
        if (arr[i][j] === arr[i][j - 1]) {
            count++;
            continue;
        }
    }
    if (count > max) {
        max = count;
    }
    count = 1;
}

for (let j = 0; j < arr.length; j++) {
    for (let i = 1; i < arr[j].length; i++) {
        if (arr[i][j] === arr[i - 1][j]) {
            count++;
            continue;
        }
    }
    if (count > max) {
        max = count;
    }
    count = 1;
}


for (let i = 1; i < arr.length; i++) {
    if (arr[i][i] === arr[i - 1][i - 1]) {
        count++;
        continue;
    }

    if (count > max) {
        max = count;
    }
}

count = 1;


for (let i = 1; i < arr.length; i++) {
    var jay = chislo;
    if (arr[i][jay] === arr[i - 1][jay + 1]) {
        count++;
    }
    if (count > max) {
        max = count;
    }
    chislo--;
}

print(max)