#include<bits/stdc++.h>
#define ff first
#define ss second
#define ll long long
#define pb push_back
using namespace std;
typedef pair<int,int> pii;


const int mod=998244353;
inline int add(int x,int y){int ret=x+y;if(ret>=mod)ret-=mod;return ret;}
inline int sub(int x,int y){int ret=x-y;if(ret<0)ret+=mod;return ret;}
inline int mul(int x,int y){return ((ll)x*y)%mod;}
inline int step(int base,int pw){int ret=1;while(pw){if(pw&1)ret=mul(ret,base);base=mul(base,base);pw>>=1;}return ret;}
inline int invv(int x){return step(x,mod-2);}

const int maxn=3e5+10;
int a[maxn];


int main(){

    freopen("triangles.in","r",stdin);
    freopen("triangles.out","w",stdout);

    int n;
    scanf("%d",&n);
    int start=1;
    if(n%2==1)start++;
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }

    sort(a+1,a+n+1);

    int j=n;
    double rez=0;
    for(int i=start;i<=n;i++){
        if(i>=j)break;
        ///cout<<a[i]<<" "<<a[j]<<" "<<a[i]*a[i]+a[j]+a[j]<<endl;
        rez+=sqrt(a[i]*a[i]+a[j]*a[j]);
        j--;
    }

    cout<<fixed<<setprecision(11)<<rez<<endl;

return 0;
}