#include using namespace std; #if __has_include() #include using namespace atcoder; #endif using ll = long long; using ld = long double; #define all(s) (s).begin(),(s).end() #define vcin(n) for(ll i=0;i>n[i] #define rep2(i, m, n) for (int i = (m); i < (n); ++i) #define rep(i, n) rep2(i, 0, n) #define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i) #define drep(i, n) drep2(i, n, 0) #define rever(vec) reverse(vec.begin(), vec.end()) #define sor(vec) sort(vec.begin(), vec.end()) #define fi first #define se second #define P pair //const ll mod = 998244353; const ll mod = 1000000007; const ll inf = 2000000000000000000ll; static const long double pi = 3.141592653589793; void YesNo(bool a){if(a){cout<<"Yes"< void chmax(T& t,const U& u){if(t void chmin(T& t,const U& u){if(t>u) t=u;} ll modPow(ll a, ll n, ll mod) { ll ret = 1; ll p = a % mod; while (n) { if (n & 1) ret = ret * p % mod; p = p * p % mod; n >>= 1; } return ret; } int main() { /* mod は 1e9+7 */ ios::sync_with_stdio(false); std::cin.tie(nullptr); cout<< fixed << setprecision(10); ll a,b; cin>>a>>b; assert(1<=a&&a<=1000000000&&1<=b&&b<=min(a,100000ll)); if(b==1){ cout< c(b); vcin(c); for(int i=0;i=1;i--){ tmp+=c[b-1]-c[i]; chmin(ans,ld(b)/ld(b-i)+tmp/ld(b-i)); } cout<