#include "soccer.h"
#include <cassert>
#include <cstdio>
#include <algorithm>
#include <vector>

#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2")

const int N = 2005;
int up[N][N], down[N][N];
void clear(int x) {
	for(int i = 0;i < N;++i)
	for(int j = 0;j < N;++j) {
		up[i][j] = 0;
		down[i][j] = 0;
	}
}
int dp[N][N];
struct rmq {
	std::vector<int> st[12];
	rmq(const std::vector<int> & v) {
		st[0] = v;
		for(int i = 1;(1 << i) - 1 < (int) v.size();++i) {
			st[i].resize(v.size() - (1 << i) + 1);
			for(int j = 0;j + (1 << i) - 1 < (int) v.size();++j) {
				st[i][j] = std::min(st[i - 1][j], st[i - 1][j + (1 << (i - 1))]);
			}
		}
	}
	int qry(int l, int r) {
		const int lg = std::__lg(r - l + 1);
		return std::min(st[lg][l], st[lg][r - (1 << lg) + 1]);
	}
};
int biggest_stadium(int N, std::vector<std::vector<int>> F) {
	for(int i = 0;i < N;++i) {
		for(int j = 0;j < N;++j) {
			if(F[i][j]) {
				up[i][j] = 0;
			} else {
				up[i][j] = 1;
				if(i) up[i][j] += up[i - 1][j];
			}
		}
	}
	for(int i = N - 1;i >= 0;--i) {
		for(int j = 0;j < N;++j) {
			if(F[i][j]) {
				down[i][j] = 0;
			} else {
				down[i][j] = 1 + down[i + 1][j];
			}
		}
	}
	int ans = 0;
	for(int i = 0;i < N;++i) {
		std::vector<int> a(up[i], up[i] + N);
		std::vector<int> b(down[i], down[i] + N);
		rmq A(a), B(b);
		auto qry = [&](int l, int r) {
			return A.qry(l, r) + B.qry(l, r) - 1;
		};
		for(int x = 0;x < N;++x) {
			for(int y = x;y < N;++y) {
				dp[x][y] = -1e9;
			}
			for(int y = x;y < N;++y) {
				if(!a[y] || !b[y]) break;
				dp[x][y] = 0;
			}
		}
		for(int x = 0;x < N;++x) {
			for(int y = N - 1;y >= x;--y) {
				dp[x][y] += qry(x, y);
				dp[x + 1][y] = std::max(dp[x + 1][y], dp[x][y]);
				dp[x][y - 1] = std::max(dp[x][y - 1], dp[x][y]);
				if(x == y) ans = std::max(ans, dp[x][y]);
			}
		}
	}
	clear(N);
    return ans;
}

#ifdef zqj
int main() {
	freopen("1.in", "r", stdin);
    int N;
    assert(1 == scanf("%d", &N));
    std::vector<std::vector<int>> F(N, std::vector<int>(N));
    for (int i = 0; i < N; i++)
    {
        for (int j = 0; j < N; j++)
        {
            assert(1 == scanf("%d", &F[i][j]));
        }
    }
    fclose(stdin);

    int res = biggest_stadium(N, F);

    printf("%d\n", res);
    fclose(stdout);
    return 0;
}
#endif