// selection_loop.cpp
#include<cstdio>
#include<cstring>
const int maxn = 17;

int main()
{
	int n, a[maxn][maxn], ans = 0;
	scanf("%d", &n);
	for(int i = 0; i < n; ++i)
	{
		for(int j = 0; j < n; ++j)
		{
			scanf("%d", &a[i][j]);
		}
	}
	for(int mask = 0; mask < (1 << n); ++mask)
	{
		int cnt = 0;
		int used[maxn];
		bool flag = true;
		memset(used, 0, sizeof(used));
		for(int i = 0; i < n; ++i)
		{
			if((mask >> i) & 1)
			{
				used[i] = 1;
				++cnt;
				for(int j = 0; j < i; ++j)
				{
					if(used[j] && a[i][j])
					{
						//printf("i = %d, j = %d\n", i, j);
						flag = false;
						break;
					}
				}
				if(flag == false) break;
			}
			
		}
		//printf("flag = %s, mask = %d, cnt = %d\n", flag?"TRUE":"FALSE", mask, cnt);
		if(flag && ans < cnt) ans = cnt; 
	}
	printf("%d\n", ans);
	return 0;
}