#include<cstdio>
using namespace std;
const int N=90,Mod=1e9+7; int n,c,a[N],ans[N],sum;
void dfs(int u,int lst) {
  if(u==c+1) {
  	long long tot=a[ans[1]]; bool flag=false;
  	for(int i=2;i<=c;i++) {
  	  if(ans[i]!=ans[1]) flag=true;
  	  tot=tot*a[ans[i]]%Mod;
	}
	//printf("%d %d\n",ans[1],ans[2]);
	if(flag) sum=(sum+tot)%Mod;
	return;
  }
  for(int i=lst;i<=n;i++) ans[u]=i,dfs(u+1,i);
}
int main() {
  //freopen("spice.in","r",stdin);
  //freopen("spice.out","w",stdout);
  scanf("%d %d",&n,&c);
  for(int i=1;i<=n;i++) scanf("%d",&a[i]);
  dfs(1,1),printf("%d",sum);
  return 0;
}