#include<cstdio>
#include<cstring>
#include<cstdlib>
using namespace std;
int n, m, dp[1 << 16], num[105], que[1 << 16], ans, dif;
inline int nextBin(void) {
	int res = 0;
	while (getchar() != '\n');
	for (int i = 0; i < n; i++)
		(res <<= 1) |= (getchar() - '0');
	return res;
}
signed main(void) {
	scanf("%d%d", &n, &m);
	for (int i = 0; i <= m; i++)num[i] = nextBin();
	memset(dp, -1, 1 << (n + 2));
	memcpy(que, num + 1, m << 2);
	for (int i = 1; i <= m; i++)dp[num[i]] = 0;
	for (int hd = 0, tl = m; hd < tl; hd++)
		for (int i = 1, top = que[hd], tmp = dp[top]; i <= m; i++)
			if (dp[top^num[i]] < 0)dp[top^num[i]] = tmp + 1, que[tl++] = top^num[i];
	for (int i = 1, tmp = dp[0] ? 2 : 1; i <= m; i++)dp[num[i]] = tmp;
	for (int i = 0; i < n; i++)dif += (num[0] >> i) & 1;
	for (int i = 0, j, diff; i < (1 << n); i++)if (dp[i] > 0) {
		for (j = diff = 0; j < n; j++)diff += (num[0] >> j) & 1 ^ (i >> j) & 1;
		ans = ((diff < dif) || (dif == diff&&dp[i] < dp[ans])) ? i : ans, dif = diff < dif ? diff : dif;
	}
	printf("%d\n", dp[ans]);
	for (int i = n - 1; i >= 0; i--)putchar('0' + ((ans >> i) & 1));
	putchar('\n');
}