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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define infinity (1000000007)
  4. #define ll long long
  5. #define ull unsigned long long
  6. #define pii pair<int,int>
  7. #define ppi pair<pii,int>
  8. #define ppp pair<pii,pii>
  9. #define pip pair<int,pii>
  10. #define pb push_back
  11. #define mp make_pair
  12. #define eps 1e-9
  13. #define s(n) scanf("%d",&n)
  14. #define s2(n,m) scanf("%d%d",&n,&m)
  15. #define s3(n,m,l) scanf("%d%d%d",&n,&m,&l)
  16. #define s4(n,m,l,x) scanf("%d%d%d%d",&n,&m,&l,&x)
  17. #define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
  18. ll pwr(ll a,ll b,ll mod) {a%=mod;if(a<0)a+=mod;ll ans=1; while(b) {if(b&1) ans=(ans*a)%mod; a=(a*a)%mod; b/=2; } return ans; }
  19. ll pwr(ll a,ll b) {ll ans=1; while(b) {if(b&1) ans*=a; a*=a; b/=2; } return ans; }
  20. ll gcd(ll a,ll b) {while(b) {ll temp=a; a=b; b=temp%b; } return a; }
  21. ll lcm(ll a,ll b) {return (a/gcd(a,b))*b; }
  22. string toString(int j){string s = "";while(j){int temp=j%10;s+=temp+'0';j=j/10;}reverse(s.begin(),s.end());return s;}
  23. ll modularInverse(ll a,ll m) {/*reminder: make sure m is prime*/ assert(false); return pwr(a,m-2,m); }
  24. const int mod=1000000007;
  25.  
  26. int n;
  27. double k;
  28. int a[2*100005];
  29.  
  30. bool possible(double x){
  31.  
  32. 	if(x<=a[1] && 2*x<=a[n+1])
  33. 		return true;
  34. 	return false;
  35. }
  36.  
  37. int main(){
  38.  
  39. 	cin >>  n >> k;
  40.  
  41. 	for(int i=1;i<=2*n;i++)
  42. 		cin >> a[i];
  43.  
  44. 	sort(a+1,a+2*n+1);
  45.  
  46. 	double lo = 0.0,hi=(double)k/(double)(n*3),mid=0.0,ans=0.0;
  47.  
  48. 	while(fabs(hi-lo)>eps){
  49. 		mid=(lo+hi)/2.0;
  50.  
  51. 		if(possible(mid)){
  52. 			ans = mid;
  53. 			lo = mid;
  54. 		}
  55. 		else hi=mid;
  56. 	}
  57.  
  58. 	ans = 3*n*ans;
  59. 	printf("%.6lf",ans);
  60.  
  61.  
  62.  
  63.  
  64.  
  65.  
  66.  
  67.  
  68. 	return 0;
  69. }
Success #stdin #stdout 0s 4244KB
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https://ideone.com/WI9yEd
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
secret

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