350A - TL

思路：

依题意模拟即可，注意等号。

代码：

#include <iostream>
#include <algorithm>
using namespace std;
const int N = 1010;
int n,m;
int a[N],b[N];
int main () {
	cin >> n >> m;
	for (int i = 1;i <= n;i++) cin >> a[i];
	for (int i = 1;i <= m;i++) cin >> b[i];
	int maxa = *max_element (a+1,a+1+n),mina = *min_element (a+1,a+1+n);
	int minb = *min_element (b+1,b+1+m);
	if ((minb-1)/2 < mina || minb <= maxa) cout << "-1" << endl;
	else cout << min (minb-1,max (mina*2,maxa)) << endl;
	return 0;
}