cf022B.cc

#include <iostream>
#include <algorithm>
using namespace std;

int N, M;
int R[30][30] = {0};

bool isEmpty( int si, int ei, int sj, int ej  ) {
	for( int i = si ; i <= ei ; ++i ) 
		if( R[i][ej]-R[i][sj-1] != (ej-sj)+1 ) return false;
	return true;
}

int main() {
	cin >> N >> M;

	for( int i = 1 ; i <= N ; ++i ) {
		char tmp[30];
		cin >> tmp;
		for( int j = 1 ; j <= M ; ++j ) {
			R[i][j] = 1 - (tmp[j-1]-'0');
			R[i][j] += R[i][j-1];
		}
	}

	int best = 0;

	for( int i = 1 ; i <= N ; ++i ) {
		for( int j = 1 ; j <= M ; ++j ) {
			for( int k = i ; k <= N ; ++k ) {
				for( int l = j ; l <= M ; ++l ) {
					if( isEmpty( i, k, j, l ) ) {
						int width = l-j+1;
						int height = k-i+1; 
						best = max( best, (width+height)*2 );
					}
				}
			}
		}
	}

	cout << best << endl;

	return 0;
}