#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> PII;
#define x first
#define y second

const int N = 1e6 + 10;
int n, m;
int ans, f[N];
PII a[N];
int al;
// 本代码未AC，8/10通过，原因未知
int main() {
#ifndef ONLINE_JUDGE
    freopen("2549.in", "r", stdin);
#endif
    cin >> n >> m;

    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++) {
            char x;
            cin >> x;
            if (x == '1') a[al++] = {i, j};
        }
    // 似乎不需要进行排序，因为上面就是按顺序输入的节点
    sort(a, a + al);

    // LIS
    for (int i = 0; i < al; i++) f[i] = 1; // DP数据初始化

    for (int i = 0; i < al; i++)
        for (int j = 0; j < i; j++)
            if (a[j].y > a[i].y) f[i] = max(f[i], f[j] + 1);

    // Dilworth
    for (int i = 0; i < al; i++) ans = max(ans, f[i]);
    printf("%d\n", ans);

    return 0;
}