样例一直解决不掉，求调！

#include<bits/stdc++.h>

using namespace std;
int n,k,sum = 0,a[25],ans = 0,bj[25];
bool prim(int ans) {
	if (ans < 2) return false;
	for (int i = 2; i*i <= ans; ++i) {
		if (ans % i == 0) return 0;
	}
	return 1;
}

void dfs(int dep) {
	if (dep == k+1) {
		for (int i = 1; i <= k; ++i)
			sum+=a[i];
		if (prim(sum)) ans++;
	}
	else {
		for (int i = 1; i <= n;++i) {
			if (bj[i] == 0) {
				bj[i] = 1;
				dfs(dep+1);
				bj[i] = 0;
			}
		}
	}
}

int main() {
	cin >> n >> k;
	for (int i = 1; i <= n; ++i)
		cin >> a[i];
	cout << ans;
	return 0;
}