#include<bits/stdc++.h>
using namespace std;
namespace my_std{
	#define ll long long
	#define bl bool
	ll my_pow(ll a,ll b,ll mod){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res=(res*a)%mod;
			a=(a*a)%mod;
			b>>=1;
		}
		return res;
	}
	ll qpow(ll a,ll b){
		ll res=1;
		if(!b) return 1;
		while(b){
			if(b&1) res*=a;
			a*=a;
			b>>=1;
		}
		return res;
	}
	#define db double
	#define pf printf
	#define pc putchar
	#define fr(i,x,y) for(register ll i=(x);i<=(y);i++)
	#define pfr(i,x,y) for(register ll i=(x);i>=(y);i--)
	#define go(u) for(ll i=head[u];i;i=e[i].nxt)
	#define enter pc('\n')
	#define space pc(' ')
	#define fir first
	#define sec second
	#define MP make_pair
	#define il inline
	#define inf 8e18
	#define random(x) rand()*rand()%(x)
	#define inv(a,mod) my_pow((a),(mod-2),(mod))
	il ll read(){
		ll sum=0,f=1;
		char ch=0;
		while(!isdigit(ch)){
			if(ch=='-') f=-1;
			ch=getchar();
		}
		while(isdigit(ch)){
			sum=sum*10+(ch^48);
			ch=getchar();
		}
		return sum*f;
	}
	il void write(ll x){
		if(x<0){
			x=-x;
			pc('-');
		}
		if(x>9) write(x/10);
		pc(x%10+'0');
	}
	il void writeln(ll x){
		write(x);
		enter;
	}
	il void writesp(ll x){
		write(x);
		space;
	}
}
using namespace my_std;
ll n;
db p[100010],sum[100010],q[100010],c;
il bl solve(db S){
	db D=sqrt(c*c*S+(1-c)*(c*S+1));
	fr(i,1,n){
		db k=(n*c+1-c)/D/sum[i];
		if((D*p[i]*k-c)>=0){
			fr(j,1,i-1) q[j]=0;
			fr(j,i,n) q[j]=(D*p[j]*k-c)/(1-c);
			break;
		} 
	}
	db now=0;
	fr(i,1,n) now+=p[i]*p[i]*(1+(1-q[i])*c*S)/(1-(1-q[i])*(1-c));
	return now<=S;
}
int main(){
	n=read();
	c=0.01*read();
	fr(i,1,n) p[i]=read();
	sort(p+1,p+n+1);
	ll all=0;
	fr(i,1,n) all+=p[i];
	fr(i,1,n) p[i]/=all;
	if(c==1){
		pf("%.7lf",1.0/p[n]);
		return 0;
	}
	fr(i,1,n) p[i]=sqrt(p[i]);
	pfr(i,n,1) sum[i]=sum[i+1]+p[i];
	db l=0,r=1e9;
	while(fabs(r-l)>1e-7){
		db mid=(l+r)*0.5;
		if(solve(mid)) r=mid;
		else l=mid;
	}
	pf("%.7lf",l);
}