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15954.cpp
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15954.cpp
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#include <cmath>
#include <vector>
#include <iomanip>
#include <iostream>
using namespace std;
int main(void) {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, k;
cin >> n >> k;
vector<int> v(n);
for (int i = 0; i < n; i++) {
cin >> v[i];
}
long double ans = 2147483647;
for (int i = 0; i < n; i++) {
vector<int> q;
int tmp = 0;
for (int j = i; j < n; j++) {
q.push_back(v[j]);
tmp += v[j];
if (q.size() < k) {
continue;
}
long double avg = tmp / (long double)q.size();
long double sum = 0;
for (int u = i; u < j + 1; u++) {
sum += (v[u] - avg) * (v[u] - avg);
}
sum /= (long double)q.size();
sum = sqrt(sum);
if (ans > sum) {
ans = sum;
}
}
}
cout << fixed << setprecision(10) << ans << '\n';
return 0;
}