int dp[30010][30];
int qian[30];
int val[30];
int main()
{
	int n, m;
	cin >> n >> m;
	for (int i = 1; i <= m; ++i)
	{
		cin >> qian[i] >> val[i];
		val[i] = qian[i] * val[i];
	}
	
		for (int j = 1; j <= m; ++j)
		{
			for (int i = 0; i <= n; ++i)
			{
			if (i >= qian[j])
			{
				dp[i][j] = max(dp[i][j - 1], dp[i - qian[i]][j-1] + val[j]);
			}
			else
				dp[i][j] = dp[i][j - 1];
		}
	}
	cout << dp[n][m];
	return 0;
}

这是我的代码，过不了，请问为什么。