#include <bits/stdc++.h>

using namespace std;

const int INF = (1 << 29) - 1;

char s[510][510];
int n, m;

int DP[4][510][510];
int up[510][510];

int rgt[510][510];
int ans = 0;

int main() {
  cin >> n >> m;
  for(int i = 1; i <= n; ++i) {
    cin >> (s[i] + 1);
  }


  for(int i = 1; i <= n; ++i) {
    for(int j = 1; j <= n; ++j) {
      if(s[i][j] == '0')
        continue;

      up[i][j] = 1 + up[i - 1][j];
    }
  }

  for(int i = 1; i <= n; ++i)
    rgt[i][n + 1] = -INF;


  for(int i = 1; i <= n; ++i) {
    for(int j = n; j >= 1; --j) {
      int &now = rgt[i][j];
      if(s[i][j] == '0') {
        now = -INF;
        continue;
      }

      now = 1 + rgt[i][j + 1];
      if(up[i][j + 1] > 1)
        now = max(now, 1 + up[i][j + 1]);

    }
  }

  for(int i = 1; i <= n; ++i) {
    for(int j = 1; j <= n; ++j) {
      if(up[i][j] > 1) {
        int now = up[i][j] + rgt[i][j] - 1;
        if(now > ans)
          ans = now;
      }
    }
  }
  cout << ans << "\n";
  return 0;
}