1 #include <iostream>
2 #include <cstdio>
3 #include <algorithm>
4 using namespace std;
5
6 typedef long long LL;
7 const int MAXN = 1e4+5;
8 const LL INF = 1e15+5;
9 LL a[MAXN], sum[MAXN], ans[MAXN];
10
11 int main()
12 {
13 int n, m;
14 while(cin>>n>>m)
15 {
16 for(int i=1; i<=n; i++)
17 scanf("%lld",&a[i]);
18 sort(a+1, a+1+n);
19 sum[0] = ans[0] = 0;
20 for(int i=1; i<=n; i++){
21 sum[i] = sum[i-1] + a[i]; //前缀和
22 ans[i] = ans[i-1] + a[i]*a[i]; //^2的前缀和
23 }
24 double Min = INF;
25 for(int i=m; i<=n; i++){
26 double tmp = (ans[i]-ans[i-m])-1.0*(sum[i]-sum[i-m])*(sum[i]-sum[i-m]) / m;
27 if(tmp < Min)
28 Min = tmp;
29 }
30 printf("%lld\n", (LL)Min); //强行转不要小数点后面，防止四舍五入
31 }
32 return 0;
33 }
