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题解：

#include<bits/stdc++.h>
using namespace std;
int dp[50010];
int a[510];
int main()
{
	int n, m;
	cin >> n;
	for(int i = 1; i <= n; i++)
	{
		cin >> a[i];
	}
	cin >> m;
	for(int i = 1; i <= m; i++)
	{
		int minn = 500000;
		for(int j = 1; j <= n; j++)
		{
			if(i >= a[j] && dp[i-a[j]] != -1) minn = min(minn, dp[i-a[j]]+1);
		}
		if(minn == 500000) dp[i] = -1;
		else dp[i] = minn;
	}
	cout << dp[m] << endl; 
	return 0;
}