HELP！！！

#include<bits/stdc++.h>
using namespace std;
int pass()
{
	return 0;
}

int main()
{
	//input
	int n, m;
	cin >> n >> m;
	int a[n][m] = {0};

	for (int i = 0; i < n; ++i) {
		char str[m];
		cin >> str;

		for (int j = 0; j < m; ++j) {
			if (str[j] == '0') {
				a[i][j] = 1;
			}
			else if (str[j] == '1') {
				a[i][j] = 2;
			}
			else {
				pass;
			}
		}
	}

	//statistics
	int max = 0;

	//Matrix ergodicity
	for (int x1 = 0; x1 <= n; ++x1) {
		for (int y1 = 0; y1 <= m; ++y1) {
			for (int x2 = x1; x2 <= n; ++x2) {
				for (int y2 = y1; y2 <= m; ++y2) {
					//Balance judgment
					int white = 0, black = 0;

					for (int i = 0; i < n; ++i) {
						for (int j = 0; j < m; ++j) {
							if (i >= x1 && i <= x2 && j >= y1 && j <= y2) {
								if (a[i][j] == 1) {
									white++;
								}
								else if (a[i][j] == 2) {
									black++;
								}
							}
						}
					}

					if (white == black) {
						int x = x2 - x1, y = y2 - y1, area;
						area = x*y;

						if (max < area) {
							max = area;
						}
					}
				}
			}
		}
	}

	//output
	cout << max << endl;
	return 0;
}

自查了一天，一直做不出来，啊啊啊