#include<iomanip> #include<iostream> #include<cstdio> #include<cmath> using namespace std; int n,k; double l[1000000]; int check(double x){ int sum=0; for(int i=0;i<n;i++){ sum+=(double)l[i]/x; } return sum; } double binary_search(double start,double end){ double ans=-1; while(start<end){ double mid=(start+end)/2; if(check(mid)<k){ end=mid; }else if(check(mid)>k){ start=mid; }else{ start=mid; if(mid==ans) return ans; ans=mid; } } return ans; } signed main(){ cin>>n>>k; for(int i=0;i<n;i++) cin>>l[i]; cout<< fixed << setprecision(2)<<binary_search(1,1e5+10); return 0; }